As an SWE I know that my brain works on problems 24/7, and not only 9 to 5 Mon-Fri. Lots of times when I stuck with some debugging or corner case or architectur

As an SWE I know that my brain works on problems 24/7, and not only 9 to 5 Mon-Fri. Lots of times when I stuck with some debugging or corner case or architecture problem - I just put it away and next morning the answer is just there in my head, ready to be typed down. As an engineering manager I can regulary see the same in my reports. Moreover, best ones are doing it on the vacation: coming back they just start typing and don't stop for 2-3 days. Normally typing/thinking cycle is at most 50/50, usually 40/60. There's one exclusion. All said things are not working if an engineer is working for two employers. When COVID mandatory WFH started, I initially thought that some of my direct or indirect reports just can't adapt to it, but it always turned out to be a second job or a personal project. I am 100% sure that 4 day workweek will lead to a lot of people in IT taking second jobs/side gigs, and it will severely impact their performance.