I’ve often wondered how many cultures use a seven day week or a week unit of any number of days in their calendar.
That’s a good one. I don’t know. Organized uniform calendars were independently developed in lots of places, then (often) imposed by conquest on other areas, possibly eliminating indigenous calendars about which we know nuttin’. Just the story of the transition to our Gregorian Calendar from the Julian Calendar is pretty convoluted, and that was done by various legislation and decrees.
In *most* of the English-speaking world, the changeover was done in September 1752 (which is why the Framers of the Constitution had two different birthdays :’), which was only 19 days long (Sept 1, 2, 14, etc was the way it was counted) in order to re-sync the calendar with the actual “calendar” of the Earth around the Sun. I can’t find the file, but the analogous conversion began in Roman Catholic countries (but just to be confusing, not all of ‘em, if memory serves) in the 17th century; Sweden (I think it was) changed later, then changed back, then changed back again, and had some extra leap days, a real mess. The last country to change (I think...) was the USSR, as the Russian Empire had steadfastly refused to, meaning that the calendar dates in Russia don’t match for that period of 150 years or so. Wowzo.