The 7 day week is completely artificial.
Days exist, defined by the rotation of the Earth.
Months exist, defined by the orbit of the moon.
Seasons exist, defined by the solstices and equinoxes.
Years exist, defined by the orbit of the Earth.
Pretty much everything else is an invention of man.
May I refer you to timecube?
If we are being even more pedantically correct about this:
1. The statement about months is kinda wrong. Solar months just happen because of the earths orbit around the sun, too, and the division by 12 is how many knuckles you can count on one hand by using your thumb.
Moon months exist, and there are 13 of them, from January to Undecember (11th month by name, but some Pope's birthdays reforms happened until we ended up with February at 28 days and no spring's start is the new year, etc.), or whatever you want to call them. But by happenstance if we talk about having a moon-month, we will probably be in a culture that uses a calendar that does not have a two-day weekend.
2. Seasons regionally exist, only.
Barely, or even none at the equator, and probably warm/cold/warm/cold, so twice as many seasons if measurable by solstice, per year, not half that many.
And Southern Hemisphere does not use a reverse "Christmas is in summer" calendar[1]
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Footnotes:
1: even if that was christmas before the popes changed it and/or christians like to feast when heathens breathren/converts did, simultenously. And historally more plausible for a time of travel to do a census.