Cut the working week to a maximum of 20 hours
guardian.co.uk
guardian.co.uk
Except that wouldn't happen. The self employed and those whose hours couldn't be tracked would work more to get a competitive advantage, encouraging widespread disobedience of the law.
It's an absolute nonsense in any case because I don't know anyone who could "share" my job with me. If I were forced into these hours, my stay-at-home-mom wife would be forced to go to work and do something she is neither any good at nor wants to do, or we'd just fall off grid, live off the land and stop contributing to the economy at large.
As you say, you certainly can't just say "right everyone, 20 hours only from now on..."