8 hours / day over 5 days, or 40 hours a week however you like, is a magic number with no real psychological basis. It certainly didn't come about for the benefit of
creatives, the subgroup of software devs who can and often do benefit from far more than 40 hours per week "working" and who only by putting in more hours can accomplish their goals. Try telling Michelangelo that if only he had forced himself to stick to 40 hours a week he could have accomplished all he did and even more greatness. Zoning out probably happens to us all, but some are quite capable of limiting it in duration and/or frequency by quite a large degree, or turning it to 'productive zoning out' whereby you progress on a relatively boring task while thinking of other things, some of which might even be what you'll do once the boring groundwork is complete. Another case, try telling a kid he can become as great as Lee Sedol by only practicing Go and playing games for a maximum of 40 hours a week. Better yet, tell Lee Sedol himself that he could get stronger by playing and studying less! And in our actual field:
https://news.ycombinator.com/threads?id=JohnCarmack et al.
It's quite possible for x work + y frustration and self loathing to be x=0 and y=30 as you hope no one notices you coming in late / leaving early and being totally vague about progress during daily meetings. I think those behaviors and 'zoning out' are mostly orthogonal to hours 'worked', though.
There's probably some agreement somewhere. I do think a lot of 80 hour, 100 hour work week boasting is just that, boasting, and surely for some doesn't really translate to that many hours of "real work". It comes from creative accounting of work hours and I think is rooted in a poor work/rest of life separation. Think about your startup for a while during dinner? I guess you're technically working, huh? Or for video game testers, your bugs filed / hour playing the game looking for bugs isn't a nice flat line with a sharp drop off after 8 hours, but a lot of people out of the industry will say "you're just playing a video game over and over for 12+ hours a day for weeks and call that work?".