"Ever since the creation, people have observed a weekly calendar. The
seven-day week (unlike the day, month, and year) has no astronomical basis.People keep time in weeks simply because God did! Even those who deny the six-day week of creation must observe it, for their biological rhythms are constructed that way by God. “The sabbath was made for man,” said Jesus (Mark 2:27).
Since God considered the truth of the literal creation week so important that He inscribed it Himself, we should believe this portion of His Word first of all." HMM