[IshKebab]

You're assuming that by working fewer hours you'd magically eliminate only the unproductive hours. That seems extremely unlikely.

I read an article years ago from someone that tried it, expecting exactly what you're expecting, but they found that proportional of their working time that was productive was about the same.

[breuleux]

It might depend on how you organize your time. I could see how working for 4 consecutive hours might have proportionally the same amount of unproductivity, but maybe splitting it in two blocks of two hours with a two hour pause in-between would work better?

[satvikpendem]

I have not found that to be the case, referring to your 2nd paragraph. In fact most of the evidence I've seen wrt <8 hour work days have been that people get as much or even more done than they thought [0].

[0] https://www.fastcompany.com/3063262/what-happened-when-i-mov...