There's no calendar that says anything about when the seventh day is and when the six days a worker are. Would they be using a calendar written by the Egyptians?
Please read Deuteronomy 5:13-14.
the hebrew calendar is in the old testament the lord mentions it in leviticus 23, 23 And the Lord spoke to Moses, saying, 2 “Speak to the children of Israel, and say to them: ‘The feasts of the Lord, which you shall proclaim to be holy convocations, these are My feasts.
The Sabbath
3 ‘Six days shall work be done, but the seventh day is a Sabbath of solemn rest, a holy convocation. You shall do no work on it; it is the Sabbath of the Lord in all your dwellings.
The Passover and Unleavened Bread
4 ‘These are the feasts of the Lord, holy convocations which you shall proclaim at their appointed times. 5 On the fourteenth day of the first MONTH at twilight is the Lord’s Passover. 6 And on the fifteenth day of the same month is the Feast of Unleavened Bread to the Lord; seven days you must eat unleavened bread. 7 On the first day you shall have a holy convocation; you shall do no customary work on it. 8 But you shall offer an offering made by fire to the Lord for seven days. The seventh day shall be a holy convocation; you shall do no customary work on it.’” did you see it mentions the 14th day of the first MONTH,those are calendar days , which means there must be a calendar for months to be known. this is not the egyptians saying this,it is GOD telling of months in which sabbaths were to be kept. The weekly sabbath being a holy convocation a day you shall do no work on because it is the sabbath of the lord ,if it were not a certain day ,how would they know which day to assemble? so there must have been a certain day which they have kept since that time.