The word "Sabbath" does not occur in the book of Genesis. It does not say the word in Scripture till Exodus 16 with Moses leading the Children of Israel in the Wilderness and being given manna, the bread of heaven.

We find in Exodus 16 starting at verse 22,
"22 And it came to pass, that on the sixth day they gathered twice as much bread, two omers for one man: and all the rulers of the congregation came and told Moses.23 And he said unto them, This is that which the Lord hath said, To morrow is the rest of the holy sabbath unto the Lord: bake that which ye will bake to day, and seethe that ye will seethe; and that which remaineth over lay up for you to be kept until the morning.24 And they laid it up till the morning, as Moses bade: and it did not stink, neither was there any worm therein.25 And Moses said, Eat that to day; for to day is a sabbath unto the Lord: to day ye shall not find it in the field. 26 Six days ye shall gather it; but on the seventh day, which is the sabbath, in it there shall be none.27 And it came to pass, that there went out some of the people on the seventh day for to gather, and they found none."

But notice verse 4,
"4 Then said the Lord unto Moses, Behold, I will rain bread from heaven for you; and the people shall go out and gather a certain rate every day, that I may prove them, whether they will walk in my law, or no." which is repeated in verse 38, "28 And the Lord said unto Moses, How long refuse ye to keep my commandments and my laws?"

Many say that humans were not told to follow God’s example or keep the day holy. But as you can see with the story of the manna, the Sabbath was already part of what God had given to man. So did Adam and Eve or their sons and daughters follow what God had given them at Creation in setting aside the seventh day and blessing it and making it holy.

The word Sabbath has its origins in the Hebrew word shabbat, from a root meaning "to cease, desist, or rest." At Creation, Genesis simply says it was the "Seventh Day", as we read in Genesis 2,
"1 Thus the heavens and the earth were finished, and all the host of them.2 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made.3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made."

Well I came across a verse that doesn't have the familiar words such as "Sabbath" to anchor our understanding. But the word did not exist at Creation and neither were there other words which we look for, such as "Week" or "Day of Preparation" to clue us in.

So what does Genesis 4 give us, lets go over Genesis 4:2-4 King James Version (KJV),

"2 And she again bare his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground.

3 And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the Lord.

4 And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the Lord had respect unto Abel and to his offering:"

So as we only have seven days, nothing called a "Week" or identifying nomenclature, when did Cain and Abel come to do their offerings. The only time they had for measure given to us, was the seven days. So what does Strongs tell us on H7093 in verse 3:

And in process H7093 of time H3117 it came to pass, that Cain H7014 brought H935 of the fruit H6529 of the ground H127 an offering H4503 unto the LORD. H3068

The KJV translates Strongs H7093 in the following manner: end (52x), after (10x), border (3x), infinite (1x), process (1x).

I.end

A.end, at the end of (of time)

B.end (of space)......

Basically.."And in the process of time" (at the end of days) "it came to pass"...at the end of the known measure of time or days, “ that Cain brought of the fruit of the ground an offering unto the LORD; and Abel, he also brought of the firstlings of his flock" (Gen. 4:3, 4).

The fact of Cain and Abel coming together for the purpose of presenting an offering to the Lord, intimates that the time when they were thus engaged was deliberate, known to and recognized by them both. The bringing of offerings by both Cain and Abel was the formal recognition of God, a act of devotion.

So what is signified by “the end of days"? Why, the end of days or time frame given at Creation, must be the end of the week, and that, of course, is the Sabbath.

Here is a better explanation from a article on the Sabbath I came across and one from another source on Creation..

"....The Sabbath From Eden To Sinai

One of the most common arguments used against the observance of the seventh-day Sabbath, is that there is no evidence of its having been observed by anyone from its institution at creation until it was given as one of the Ten Commandments. Those who raise this argument would have us believe that all of history from Eden to Sinai passed without one single Sabbath being kept.


It is the purpose of this study to examine the records of Scripture and history to determine once and for all whether it is true that the Sabbath was not observed between Adam and Moses, or whether the real truth is that there is considerable evidence of Sabbathkeeping in the books of Genesis and Exodus before the giving of the Decalogue.

In addition to Scripture, we shall call as witnesses many authors, men who were not at all biased in favor of the seventh day, but whose honest statements support what we believe to be the truth.

The Sabbath was created at the very beginning of human history. In Genesis 2:1-3 we read that God blessed and sanctified the seventh day. The Hebrew word translated sanctified in Genesis 2:3 and hallowed in Exodus 20:11 is qadash, a word meaning to hallow, to pronounce holy, to consecrate, to set apart for holy use.1

There is no denying that God was here setting aside the Sabbath as holy time. Is it logical to believe that God first created man, then the Sabbath, and then failed to mention to man that the seventh day was holy time? Certainly not! God must have immediately explained to Adam all about His sacred seventh day. We might say that God preached a sermon to Adam and Eve on the first Sabbath of human history, telling them how to observe His day as He wanted it to be observed.

Jonathan Edwards says in one of his sermons: What could be the meaning of God’s resting the seventh day, and hallowing and blessing it, which He did, before the giving of the fourth commandment, unless He hallowed and blessed it with respect to mankind? . . . And it is unreasonable to suppose that He hallowed it only with respect to the Jews, a particular nation, which rose up above 2000 years after.3

In Mark 2:27, Jesus says: “The Sabbath was made for man.” The Greek has an article before man, so the phrase could be rendered, “The Sabbath was made for the man.” This is a likely reference to Adam, the first man and representative of the whole race that descended from him. This reasonable conclusion that Adam kept the Sabbath

These are sensible and logical conclusions. It is just not reasonable to think that God would make the Sabbath for man and then keep it from him for over 2000 years until Moses. So the only fair conclusion is that Adam and Even were keeping the Sabbath from the very beginning.

The very fact that the seven-day week existed, is good evidence the Sabbath also existed. Joseph Scalinger is quoted as saying: ‘The septenary arrangement of days was in use among the Orientals from the remotest antiquity.’7 The arrangement of time into weeks of seven days carries with it the Sabbath, and Scaligers statement is only one of many from authorities that the seven-day week is as old as the human race.

Here is another valuable statement from a magazine that the week is a time unit that, unlike all others, has proceeded in absolute invariable manner since what may be called the dawn of history.8
A week of seven days is frequently met with in Scripture. In Genesis 7:4 and 8:10 and 12 we see that Noah was acquainted with a seven-day week. Unless the Sabbath was their pivot of time, people then could not have used such a measure of days. In fact, the marginal rendering of Genesis 7:10 is ‘on the seventh day,’ a reference to nothing but the Sabbath. We may be sure that Noah, a just man who walked with God (Genesis 6:9), knew about and kept God;s seventh-day Sabbath.

In Genesis 29:27-28, we read that Jacob fulfilled a week for Rachel. The week here is not synonymous with the seven years Jacob served Laban for Rachel, nor does it mean seven years passed before Jacob married Rachel. The language shows Jacob married Rachel one week after he had married Leah, and then he served Laban another seven years, as explained in verses 29-30.

In Genesis 50:10, we find that Joseph mourned for his father Jacob seven days, that is, one week. So Joseph knew about the seven-day week.

Exodus 7:25 mentions a seven-day period in the time of Moses just before the Exodus. This is certainly an exact week, for we read, ‘seven days were fulfilled.’ In addition, Numbers 12:14-15 mentions a seven-day period following Israels departure from Egypt and before they arrived at Mt. Sinai.

Again, in Judges 14:10-18, we read that Samson’s marriage feast lasted for seven days, another reference to the week.

Once again, in Job 2:13, we are told that Job’s three friends sat and grieved with him for seven days and seven nights a complete week.

So it is obvious that a seven-day week with the seventh-day Sabbath was familiar to the patriarchs…..
Martin Luther wrote: Adam . . . held the seventh day sacred; that is, he taught on that day his own family.10 Luther is right. Having been told by God that the Sabbath was to be observed, he not only did so himself, but he certainly would have taught his family by precept and example to do the same.

This is proven in Genesis 4:3: And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD, and in verse 4: And Abel, he also brought of the firstlings of his flock, and of the fat thereof.

The words ‘in process of time’ are translated from the Hebrew mikkets yamim, meaning at the end of the days. This can only be telling us that on the Sabbath, Cain and Abel, with the rest of Adams family, gathered to worship God. Adam Clarke says, it is more probable that it means the Sabbath, on which Adam and his family undoubtedly offered oblations to God, as the divine worship was certainly instituted, and no doubt the Sabbath properly observed in that family.11 Jamieson, Fausset, and Brown say it was probably on the Sabbath.12

Another commentary has this to say: More likely this phrase denotes the Sabbath . . . the end of the weekdays. And as it is plain that the Sabbath was observed as holy time since its formal institution by God in Paradise, it was doubtless kept holy by such appointments of worship as would distinguish the day.13

There is nothing in nature that can be pointed to as measuring the week; only the Sabbath marks it. And only the Sabbath could come at the end of days. Clearly, the family of Adam and Eve kept every Sabbath sacred unto the Creator.
...."
http://www.giveshare.org/HolyDay/sabbathfromedentosinai.html

Here is the one from Creation site...


"...An often-overlooked testimony to the fact of creation is
the strange phenomenon of the seven-day week. Almost
universally observed in the present world and often observed
in the ancient world, it is so deeply rooted in human
experience and so natural physiologically that we seldom
think about its intrinsic significance.

All the other important time markers in human life are
clearly based on astronomical and terrestrial constants. The
day, for example, is the duration of one rotation of the
earth on its axis; the year is the duration of one orbital
revolution of the earth about the sun; the month is the
approximate interval between new moons; the seasons are
marked by the equinoxes and solstices.

But the week has no astronomical basis whatever! Yet we
order our lives in a seven-day cycle, doing certain things
on Monday, certain other things on Tuesday, and so on
through the week. Furthermore, the common pattern is one of
six normal working days, then a day of rest or change, then
six normal days again, and so on, with the special day
regarded as either the last of the seven preceding it, or
the first of the seven following it.

How could such a system ever have originated? Most
encyclopedias and reference books treat the subject very
superficially, if at all. One can easily find extensive
discussions about the length of the year and the length of
the month in different eras and cultures, but it is very
difficult to locate information about the week. Most of the
discussions that do try to deal with it attribute the origin
of the week to the use of "market days," pointing out also
that the interval between market days was different in
different nations, though rarely varying more than a day or
so above or below seven days. With the exception of an
occasional Biblical scholar, almost none of these writers
even considers the obvious explanation—namely, that the
seven-day week was established by God Himself, at the
beginning!

Every effect must have an adequate cause, and the only cause
which is truly able to account for such a remarkable
phenomenon as the week is that it was established at
creation and has been deeply etched in the common human
consciousness ever since. Even if the week is noted in some
cultures in terms of regular market days, this still does
not explain how the market days happened to cluster around
every "seventh" day, instead of every fifteenth day or
nineteenth day or something else. Besides, there were
various ancient nations whose weeks were quite unrelated to
any marketing customs.

A related phenomenon, equally remarkable, is the almost
universal significance attached to the number "seven," as a
number speaking of completeness, usually with special
religious overtones. This number is not "natural" in any
physical way. It would be more natural to use the number
"ten" (the number of a man's fingers), or the number
"twelve" (the number of months in the year), or perhaps the
number "365," to represent fullness. Why "seven"? Yet
"seven" is everywhere the number of completeness.

Many people believe that the custom of a weekly day of rest
began with Moses, when he incorporated Sabbath observance
into the Ten Commandments. However, there is considerable
evidence that Sabbath observance existed in both Israel and
in other nations long before Moses. The Word of God makes it
plain that it was established by God Himself, in
commemoration of His completed creation, and that it has
been observed as a special day, at least by some, ever
since. Here is the record:


Thus the heavens and the earth were finished, and all the
host of them, and on the seventh day God ended His work
which He had made; and He rested on the seventh day from all
His work which He had made. And God blessed the seventh day,
and sanctified it: because that in it He had rested from all
His work which God created and made (Genesis 2:1-3).

God "rested" after finishing His work of creating and making
all things in the universe in the six days just completed.
His rest was not because of fatigue (note Isaiah 40:28), but
was simply a cessation of His creative activity.

And then God blessed and sanctified the seventh day! He
declared it to be a holy day, a day peculiarly the Lord's
Day. The six days had been occupied with His creation; one
day should be occupied with the Creator. He frequently
referred later to the day as "my Sabbaths" (e.g., Exodus
31:13).

That the children of Adam, even after the expulsion from
Eden, continued to regard every seventh day as a day of rest
and worship is clearly implied in the story of Cain and
Abel.


And in process of time it came to pass, that Cain brought of
the fruit of the ground an offering unto the Lord. And Abel,
he also brought of the firstlings of his flock and of the
fat thereof (Genesis 4:3, 4).

On this particular day, Cain was not tilling the ground, as
he normally did, nor was Abel tending his sheep. On this
day, they met with the Lord and brought Him all offering.

And what day was that? The phrase "in process of time" is,
literally, "at the end of the days" ("process" = Hebrew qets
= "end"; "time" = Hebrew yamim = "days"). The day on which
they brought their offerings was the day "at the end of the
days," and this clearly can be nothing but the seventh day,
the day which God had blessed and hallowed.

The story of Noah contains many allusions to the seven-day
week. Note the following in Chapters 7 and 8 of Genesis:

1."For yet seven days, and I will cause it to rain upon the
earth" (7:4)
2."And it came to pass after seven days that the waters of
the flood were upon the earth" (7:10)
3.Forty weeks later (280 days—compare 7:11; 8:3, 4, 5, 6)
Noah sent forth the dove and the raven (8:7, 8)
4."And he stayed yet other seven days; and again he sent
forth the dove" (8:10)
5."And he stayed yet other seven days; and sent forth the
dove " (8:12)
6.Noah and his family left the ark exactly 371 days, or 53
weeks, after they had entered it (compare verses 7:11; 8:3,
4; 8:14).

Whether these repeated references to actions taken every
seven days imply that they all took place on God's rest day
is not stated, although it does seem probable. In any case,
it is clear that both God and Noah were ordering events in
terms of a seven-day cycle.

During the centuries from Noah to Moses, there was little
occasion to refer in the Bible to the week as such. However,
there do at least seem to be two allusions to it, in the
story of Jacob and Leah ("fulfill her week"—Genesis 29:27,
28) and in the story of Jacob's burial (Genesis 50:10).

Whatever form of Sabbath observance might have been
practiced by the early patriarchs, it is probable that the
long servitude in Egypt caused many to forget its religious
significance, even though the weekly cycle was still
followed. When the time came for God to redeem His people,
however, He began to remind them of its importance. In
preparation for the great Passover deliverance, He
commanded: "Seven days shall ye eat unleavened bread,—And
in the first day there shall be an holy convocation, and in
the seventh day there shall be an holy convocation to you;
no manner of work shall be done in them, save that which
every man must eat, that only may be done of you." (Exodus
13:15, 16). It is interesting that, in this preparation for
the incorporation of the Sabbath into the Ten Commandments,
both the First Day and the Seventh Day were days of rest and
worship!

Soon after this, the Israelites were strongly reminded that
a seventh day each week was intended to be a day of rest, in
the experience of the manna (Exodus 16:4, 5, 25-30), which
fell for six days each week and was withheld by God on the
seventh. Finally, Sabbath observance was incorporated as the
fourth in the array of Ten Commandments recorded for Israel
by the very finger of God on tables of stone (Exodus
31:18).


Remember the Sabbath Day to keep it holy. Six days shalt
thou labour, and do all thy work: But the seventh day is the
Sabbath of the Lord thy God: in it thou shalt not do any
work,—(Exodus 20:8-10).

It should be stressed again that the Sabbath observance was
by no means established here for the first time. The
Israelites, however, were now commanded to remember the
Sabbath and to keep it holy, as it should have been since
God so pronounced it following the creation. The Lord's holy
day may have been neglected by God's chosen people, or even
forgotten altogether by most other nations, but it was still
God's primeval commandment. At this time, God stressed again
that the basis for the commandment was not regional but
universal, relating to the entire creation. "For in six days
the Lord made heaven and earth, the sea, and all that in
them is, and rested the seventh day: wherefore the Lord
blessed the Sabbath Day, and hallowed it." (Exodus 20:11). A
commandment intended for all people should certainly be
obeyed by the chosen people!

With the passing of the centuries, the Sabbath eventually
became almost exclusively associated with the religious
ceremonies of the nation Israel, even though the Creator had
hallowed it originally for all men. When that Creator
eventually became man, however, in the person of Jesus
Christ, He stressed that it had never been intended as a
mere Jewish religious ritual, as the Pharisees had distorted
it, but for the good of all men. "The Sabbath was made for
man, and not man for the Sabbath" (Mark 2:27). All men
needed to have a day of rest and worship, for their own
physical good, and to regularly remind themselves of the
great truth of creation, for their spiritual good. And they
needed to remember continually that the one who came in to
redeem them is also the one who had created them.
"Therefore, the Son of man is Lord also of the Sabbath," He
said (Matthew 12:28).

It was appropriate, therefore, that after Christ's death and
resurrection, Christians from every nation soon began once
again to observe one day in every seven as a day of rest, as
they heard and believed the gospel of Christ. Now, however,
there were two great works of God to commemorate, the
completion of creation and the completion of redemption. As
Christ had long ago finished the work of creation
(Colossians 1:16) so He could now report once again to the
Father: "I have finished the work which thou gavest me to
do" (John 17:4). This work was climaxed with the great
victory cry on the cross: "It is finished!" (John 19:30).

For a time, Jewish Christians continued to participate both
in the synagogue services on the seventh day each week
(e.g., Acts 17:2) and also in Christian services on the
first day of the week (Acts 20:7). Eventually, as they were
more and more excluded from the synagogue, they observed the
Lord's day only on the first day of the week (I Corinthians
16:2), thereby honoring Christ simultaneously as both
Creator and resurrected Savior.

There was discussion for a long time (continuing in some
degree even today) as to whether Christian churches, once
they were completely separated from the Jewish assemblies,
should observe the Lord's day on the seventh day of the
week, as the Jews did, or on the first day of the week, as
the day of Christ's resurrection. Without entering into this
particular discussion, the important point to note here is
the fact that Christians never even questioned the necessity
for a weekly "rest day" on which especially to honor the
Lord. That need was taken for granted, regardless of whether
the "Sabbath" was to be observed on Saturday or Sunday.
("Sabbath," in Hebrew means neither Saturday nor Sunday,
neither seventh day nor first day, but rest day!).

In view of the chaotic state of ancient chronology, there is
obviously no way of knowing which day of the modern week is
an exact multiple of seven days since God's first rest day.
Those Christians who worship on Saturday believe that the
Sabbath cycle has been kept intact ever since the creation
and so they follow the practice of today's orthodox Jews,
who make the same assumption. Other Christians, however,
point out that the present Jewish calendar was not
established until the fourth century A.D., so there is
neither historical nor scientific basis for insisting that
our present Saturday was the primeval Sabbath. Some
Christian writers have argued that our modern Sunday was the
ancient Sabbath and others have maintained that the day of
the week on which the Sabbath fell actually changed from
year to year, being affected by Sabbaths other than the
weekly Sabbath, including one which extended for two days
each year. The "long day" of Joshua (Joshua 10:13, 14) also
must have affected the weekly cycle in some as yet uncertain
fashion. In any case, the important consideration is the
fact of a weekly "Lord's Day," rather than the particular
day of the modern weekly cycle on which it is observed.

It is significant that the Ten Commandments, representing
God's ineffable and unchanging holiness as they do, even
though specifically written down in the Mosaic law for
Israel's sake, are also written in the consciences of all
men (Romans 2:14, 15). Consequently, these commandments were
accepted and applied in the New Testament as well (e.g.,
Romans 13:9; Ephesians 6:2; etc.).

This affirmation is clearly implied for the Sabbath
commandment in particular. "For He spake in a certain place
of the seventh day on this wise; and God did rest the
seventh day from all His works.—There remaineth therefore
a rest to the people of God." (Hebrews 4:4, 9). In this
passage in Hebrews (verses 1-11), the English word "rest"
occurs nine times. All except one of these are translations
of essentially the same Greek word (katapausis), implying
rest from labor. The exception is in verse 9: "There is yet
reserved therefore a Sabbath rest (Greek sabbatismos,
derived from sabbaton, "Sabbath") to the people of God."
This is the only occurrence of this particular word in the
New Testament.

In context, the writer is showing that the ultimate "rest"
for God's people, which was typically portrayed by God's
rest after creation and which was therefore typified by
every weekly Sabbath observance, was not attained in Canaan
under either Joshua or David, and was still reserved for the
future even after Christ had returned to heaven and the
Christian era had begun. Since the antitype is yet future,
therefore, the type must still be in operation, just as the
animal sacrifices in the temple did not cease until Christ
"had offered one sacrifice for sins for ever." (Hebrews
10:12). This fact, combined with the evident fact that all
the early Christians continued to observe a weekly "Lord's
day," and that nowhere in the New Testament was it stated
that "Sabbath" observance should cease, makes it clear that
this commandment, like all the Ten Commandments, applies in
the Christian dispensation as well as in the Mosaic
dispensation, though not with the same applications and
penalties that related specifically to the Mosaic
ordinances. As a matter of fact, God's people will continue
to observe a weekly Sabbath even in the coming kingdom age
(note Isaiah 66:22, Ezekiel 46:3).

All of this is the tremendous testimony of the seven-day
week and, especially, of the day of rest which marks its
boundaries. Its very existence can only be explained by the
reality of a primeval six-day completed creation! God
desires that we never forget that He is both our Creator and
Redeemer, and also that we continually look forward to the
eventual fulfillment of all His creative and redemptive
purposes, when they are finally consummated in that eternal
Rest for all the people of God in the ages to
come.....http://www.icr.org/article/creation-seven-day-week/

I would say you are preaching mainly to the choir here at Maritime.