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.