[matwood]

Unless people are machines, it's incorrect to strictly equate hours with productivity. What actually happens is there is quite a bit of slack time in the typical day. Going to 4 days/week is applying a forcing function[1] to remove some of this slack time and given it back to employees.

I think a better question is how much of this slack time is necessary to reach the current productivity levels, and how much is just...slack?

[1] There are a lot of anecdote stories where people have a kid which limits their available time, and suddenly they are more productive than they have ever been during that small time window and get their startup off the ground etc...