That makes since, when sundown came the Jews gathered at Temple,
Like getting off work in Friday and likely not going back to work until Sunday..
But with so many calendars (AM/BCE-CE/AD) and losing 11 days in the Gregorian (the most accurate calendar btw) how are you certain you are keeping the same Sabbath as Adam (who by the way wasn't under Law, nor was Noah) ?
Well the obvious answer is why were the Jews so strict on the observance of the Sabbath, even with all the changes in name etc.. and you can see they were intent on keeping the seventh day as that was the 4th Commandment, not any other day. We see in scripture how God clearly pointed to the Sabbath and made clear what day it was in several ways as we see with the manna:
Exodus 16:4-28 King James Version (KJV)
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.
5 And it shall come to pass, that on the sixth day they shall prepare that which they bring in; and it shall be twice as much as they gather daily.
6 And Moses and Aaron said unto all the children of Israel, At even, then ye shall know that the Lord hath brought you out from the land of Egypt:
7 And in the morning, then ye shall see the glory of the Lord; for that he heareth your murmurings against the Lord: and what are we, that ye murmur against us?
8 And Moses said, This shall be, when the Lord shall give you in the evening flesh to eat, and in the morning bread to the full; for that the Lord heareth your murmurings which ye murmur against him: and what are we? your murmurings are not against us, but against the Lord.
9 And Moses spake unto Aaron, Say unto all the congregation of the children of Israel, Come near before the Lord: for he hath heard your murmurings.
10 And it came to pass, as Aaron spake unto the whole congregation of the children of Israel, that they looked toward the wilderness, and, behold, the glory of the Lord appeared in the cloud.
11 And the Lord spake unto Moses, saying,
12 I have heard the murmurings of the children of Israel: speak unto them, saying, At even ye shall eat flesh, and in the morning ye shall be filled with bread; and ye shall know that I am the Lord your God.
13 And it came to pass, that at even the quails came up, and covered the camp: and in the morning the dew lay round about the host.
14 And when the dew that lay was gone up, behold, upon the face of the wilderness there lay a small round thing, as small as the hoar frost on the ground.
15 And when the children of Israel saw it, they said one to another, It is manna: for they wist not what it was. And Moses said unto them, This is the bread which the Lord hath given you to eat.
16 This is the thing which the Lord hath commanded, Gather of it every man according to his eating, an omer for every man, according to the number of your persons; take ye every man for them which are in his tents.
17 And the children of Israel did so, and gathered, some more, some less.
18 And when they did mete it with an omer, he that gathered much had nothing over, and he that gathered little had no lack; they gathered every man according to his eating.
19 And Moses said, Let no man leave of it till the morning.
20 Notwithstanding they hearkened not unto Moses; but some of them left of it until the morning, and it bred worms, and stank: and Moses was wroth with them.
21 And they gathered it every morning, every man according to his eating: and when the sun waxed hot, it melted.
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.
28 And the Lord said unto Moses, How long refuse ye to keep my commandments and my laws?
Now as to the same Sabbath as Adam from Creation, God clearly did not hide the process of Creation from him, especially if they were talking in the Garden. Now here is
a article on that point I came across...
"By surprise, science has discovered amazing seven-day cycles in the very building blocks of plant and animal life. These newly found sevens, or "septans," also lie buried in us humans -- deep in our metabolic, hormonal, and neuronal networks. This startling discovery has wide-ranging effects that you will want to understand. The following article explores those effects by answering three questions. First, does the formerly unknown, automatic rhythm of sevens hold the secret to one of history's most perplexing enigmas -- the origin of the seven day week? Second, what could these innate, autonomous rhythms mean for us? And lastly, what will this new knowledge tell us about the biblical Sabbath and the Creator God?
Society's seven-day calendar week is the only major rhythm of human activity that is totally oblivious to external nature. This so-called "social week" rests on mathematical regularity alone. We may casually assume that our week is really a division of the moon cycle. If that is our assumption, we forget that the lunar cycle is not a twenty-eight-day cycle, but approximately twenty-nine days, twelve hours, forty-four minutes and three seconds -- or 29.5306 days between new moons. A precise quarter of the lunar cycle amounts to the uneven figure of 7.38625 days. So any week using that true length would begin at different times of the day every time the cycle started. There is just no way to neatly divide the lunar cycle into weekly blocks of complete days.
Then what about the sun? Doesn't the cycle of seven relate to the center of our solar system? Again, no! The 7-day week is also independent from the annual solar cycle of 365 1/4 days. A "year" of 52 weeks would have just 364 whole days. Nor is the week in harmonic sympathy with the star year of 366 1/4 days. Star days or "sidereal days" are about four minutes shorter than solar days (an observer will see a particular star at the same position four minutes earlier on successive nights). In short, there are no known external rhythms in nature that could explain the near universal existence of the seven day social week.
Yet, the importance of the seven-day week -- or heptad, a series of seven -- is monumental....Apart from the biblical record, historians have had difficulty placing the precise beginning of the seven-day week. It is simply acknowledged as an ancient practice of very early origin in the evolution of civilization."...https://sabbathsentinel.org/2019/08/15/the-amazing-7-day-cycle-part-1/
