My boss always quotet that he is happy if we are able to be 60% efficient. A lot of time is wasted for the morning coffee and some time after lunch break. A 4 hour workday would make me come to work Ready and finish with at max a short break in between. I would say in about 5 hours of constant work I would definitly do more on average than with 8.
Btw I tried 32/h weeks & 3/4/5h days I never did less work in the end than with 8
Btw I tried 32/h weeks & 3/4/5h days I never did less work in the end than with 8