IME most people don't have more than 4 (maybe 5) hours of effective heavy cognitive / creative energy in a given day. Of course YMMV, and it's common to have periods of sustained output when deeply committed to and energized by something, but over the long haul, week in, week out, splitting the workday into roughly 8h sleep, 8h work, 8h everything else, with 2/7 days off plus many holidays and some weeks of paid vacation seems like a reasonable default to me -- for the traditional salaried role. If your preferences deviate much from that baseline, the entrepreneurial / consulting / fractional approach would probably be better aligned.
Only having 4-5 hours of effective cognitive energy per day is exactly why I would want fewer work days and more off days. Because that "8 hours every thing else" is not the same as the 8 hours of work, you've already blown your cognitive load.
