If this were entirely true, businesses wouldn't be open from 9am-5pm but would have three 8-hour shifts throughout the day and run 24/7 and simply outcompete companies that are only open 9-5. The "best" companies would have even longer shifts and more complex schedules, with fewer employees.
9-5 isn't the 'optimal'. It's simply what is 'most common' for a diurnal society. Nobody is driving around town looking to get a hair cut at 3am and staring at an IDE from 1pm-5pm trying to solve a bug isn't making you any more efficient than thinking about the problem while cooking an early dinner.
Humans do suffer fatigue - both mental and physical - and proper lengths of rest helps both kinds.
I posit that happier employees are more likely to trend their work/life balance in favor of work if they enjoy their work and enjoy their company. Unhappy employees will skirt by on the bare minimum required knowing that hiring/training a new employee isn't worth the cost of firing them.
Sure, there are lots of reasons beyond Homo Economicus thinking for why we work the way we do. Laws, cultural expectations, and so on. I just don't see results-based work displacing the current norms broadly enough to make a difference, and if it does in fact result in better productivity I expect that to be eaten by competition/profit rather than going to workers as free time, in the long (medium, even) run, absent some pretty massive shifts in culture, especially with international competition in the mix.
9-5 isn't the 'optimal'. It's simply what is 'most common' for a diurnal society. Nobody is driving around town looking to get a hair cut at 3am and staring at an IDE from 1pm-5pm trying to solve a bug isn't making you any more efficient than thinking about the problem while cooking an early dinner.
Humans do suffer fatigue - both mental and physical - and proper lengths of rest helps both kinds.
I posit that happier employees are more likely to trend their work/life balance in favor of work if they enjoy their work and enjoy their company. Unhappy employees will skirt by on the bare minimum required knowing that hiring/training a new employee isn't worth the cost of firing them.