I could imagine some collective action not organized by government, for example to write a "6-hour day manifesto", share it on networks, have people sign it, wear t-shirts, choose a day when you celebrate the idea... i.e. gradually introduce the idea to the general public. (Perhaps even edgy t-shirts, such as "I only work 6 hours a day, but I spend 8 hours at work to appear busy. And so do you.") So that people notice that others share their opinions.

Sometimes memes have power (but it is difficult to engineer them properly). I believe that jokes contributed to the fall of Soviet Union, so perhaps jokes could make 8-hours day go away. Just imagine if average people would start saying: "So, you also work at a company where people pretend to work 8 hours a day? Me too." Maybe if laughter became an automatic reaction to saying "8 hours", something would change.