Notice the following about parashath hashabbath, the paragraph that describes the seventh day of creation, Genesis 2:1-3: it does not say “and there was morning and there evening, the seventh day,” or “the sabbath day.” This is unusual because all the other days are concluded with such a formula. Further, all though it does mention that God finished his work and desisted, and that he blessed the seventhg day and sancytified it, it is never reffered to as “the Sabbath.” This is even more unusual when you consider that many of the siginifcant creations are then “named” by God: The light was called day, the darkness night, the dry land earth and the firmament heaven, the gathering of the waters seas, and man Adam, who in turn names all of the animals and his wife, twice, and she names a number of children. Yet with all of this formal naming, the seventh day would have to wait.
Further, the qiddush for the Sabbath is contradictory: does the sabbath commemorate the Creation, or the Exodus?
And a related question: If a gentile who keeps the Sabbath is liable to the death penalty, why is keepin the Sabbath not counted among the seven Noahide prohibitions?
The answer to all these questions is that the seventh day indeed was holy since Creation, but until the Exodus and the giving of the Torah it was not the Sabbath in the sense that there was a national entity capable of truly understanding and experiencing the day in a way meaningful to mortals. Thus, the Creation account does not yet refer to the seventh day as the Sabbath, nor does it say that the day was completed, so to speak, because there was no Jewish people.
Thus, the qiddush rightly refers to the Sabbath day as a commemoration of the Creation, but then as a commemoration of the Exodus, and of course the gentiles were never commanded not to observe the Sabbath; rather, our sages declared that a gentile who desists from work on the Sabbath is liable to death in order to stress that the non-Jewish world should not seek to create religious behaviors.
In Hebrew, when it says that something happened “during the days of so and so,” it means when he was the dominant personality. For example, if he was a king, during his reign and after the death of his predecessors, or as in Isaac, when it says that there was a famine in his days, it was after Abraham had passed away. So too, when Maimonides writes that idolatry started in Enosh’s days, it means after Adam and Seth had died. Adam died in the year 930 from creation, while Seth died in 1042, and Enosh died in 1140, Noah was born in 1056 and Enoch, Noah’s great-grandfather, was “taken” in 987. Thus, in his commentary to the latter verse, Rashi is saying that Enoch died before humanity descended into idolatry, which would be in the next century, possibly in the fourteen years before Noah’s birth, or the subsequent years.