There was once a movement for a six-hour week.

There were lots of movements like that -- see e.g. this from 1993. France at the moment has the legal 35-hour week.

However these movements, at least historically, were mostly aimed at fighting high unemployment (and probably low demand, too). I think VW workers in Germany had effectively a four-day week during the few years of high unemployment, but when unemployment went down the four-day week ended.