The 8-hour-workday and 5-day-workweek movements were largely independent in time, and while there was some overlap in terms of both implementation and in terms

The 8-hour-workday and 5-day-workweek movements were largely independent in time, and while there was some overlap in terms of both implementation and in terms of the populations demanding them, they really came from different places. People first started getting into the 8-hour workday at the beginning of the 19th century, and it was largely driven by workers, tradesmen, and utopian communists who wanted life to consist of more than just working from the moment they woke to the moment they collapsed into sleep. "8 hours work, 8 hours rest, 8 hours sleep" was the sort of slogan that went in to that. Working too much each day just sucks. The 5-day workweek was at the beginning of the 20th, and was much more tied into the Great Depression, automation, and managing employment as a civilization. While people have come to enjoy the quality-of-life improvements associated with the existence of a "weekend", it wasn't really the motivation for the shift so much as limiting the work done per worker to offset the decreased labor demand associated with increased productivity. (Although, practically speaking, a lot of the actual regulations that encourage employers to only work people 8 hours a day date/40 hours a week date to this time in the US.)