Zvi Mowshowitz put the concept of "slack" well: https://thezvi.wordpress.com/2017/09/30/slack/
Going to a 4 day work week would bring the weekly productivity to the level of a 5 day week from the early 2000s while also providing a "virtual" wage increase.
I don't really see companies flocking to sign up.
You could also consider 10 hour four day weeks, though I guess at 10 hours many would see fatigue affecting their work.
I don't find that 10 hours fatigues me, it feels the same as an eight hour day anyway.
US working hours are nuts, IMO.
On the other hand it's possible that a 10h work day becomes less productive than an 8h one if applied long term. Of course it depends on the actual job but it wouldn't leave much time for anything personal. For a lot of jobs 10h shifts sounds like looking for trouble.
Even now, programming on salary, I'd rather do 4 tens, 7-5. The overhead of commuting is what kills me, and it'd actually be less traffic if I went in earlier. Besides, those two hours before everybody else gets there could be more productive than the whole rest of the day.
Even a short commute just kills me. This is why WFH is so effective IMO. Up between 5am and 6am. Workout, then work. Those few hours in the morning before anyone else gets in is when I do most of my 'work' for the day. The rest of the day is meetings, answering questions, etc...
Because many companies are already getting 5x10 out of their salaried employees. They don't want to lose that extra work.
8 hour days are probably a good balance between how much work you can productively put in during one day and the auxiliary time. Increasing the number of hours per day would probably decrease productivity via fatigue. Decreasing the hours wouldn't bring much of a benefit for the worker since the auxiliary time stays mostly the same (you still commute).
A good chunk of the lost productivity would probably be offset by higher worker satisfaction.
https://www.mercatus.org/system/files/helland-tabarrok_why-a...
Most important and revealing graph in the entire book
https://marginalrevolution.com/marginalrevolution/2019/05/wh...
As well as that you have growing land use regulation making certain types of housing illegal, e.g. apartments or houses below a certain area, or flophouses/SROs. Zoning more generally does this everywhere. Most of the residential buildings in Manhattan would be illegal to build today. So land holders capture much of the gains in productivity and that doesn’t show up in the labour share of productivity growth. But land ownership is extremely widespread; this is the lower middle class and up, not just the rich capturing increases in productivity.
Less important but still significant is that due to the US tax code’s treatment of benefits compensation has gone up more than wages have. The cost of health insurance has gone up enormously since the 70’s, A’s has what you get for your money.