@cell
Claude AI says:
Japan's adoption of the 7-day week is actually a relatively recent development, occurring during the Meiji period (1868-1912) as part of Japan's modernization efforts. Before that, Japan used a completely different time system.
Traditional Japanese time-keeping used a variety of cycles:

A 6-day week called the rokuyō (六曜), used for determining lucky and unlucky days
The 10-day cycle called the jun (旬), divided into upper, middle, and lower periods
A complex time system that divided the day into 6 daytime and 6 nighttime units that varied in length with the seasons