Turn the argument around. A certain sect of Christianity has said it has the authority to change the Sabbath day from the seventh day to the first day in spite that there is a lack of scripture to do that. If the seventh day is abrogated in the mosaic law then no day is more sacred then another but the seventh day is declared holy at the finish of creation.
The Hebrew Sabbath has not changed. The Hebrew does not have the liberty to change it. But to observe the Sabbath means to stay home and forsake any work not necessary. It does NOT mean to get all dolled up and "go to church."
The implementation of the commandment was:
"See, for that the LORD hath given you the sabbath, therefore he giveth you on the sixth day the bread of two days; abide ye every man in his place, let no man go out of his place on the seventh day" (Ex. 16:29 AV). There it is, observe/keep the Sabbath, or not? Under Moses, the penalty was death. Before Moses, there is no indication in Scripture that anyone kept or was commanded to keep the Sabbath. None. Any thing otherwise is simply opinion. But the Bible does say:
"For when the Gentiles, which have not the law, do by nature the things contained in the law,
these, having not the law, are a law unto themselves:
Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;..." (Rom 2:14-15 AV).
Did the Gentiles from Adam on observe the seventh day? There is simply no evidence, no information, and you cannot form a doctrine on lack of information.