I like working long hours, but 6 hours is the absolute max for the majority of people for intense intellectual or creative work for a sustained period of time.

Most super prolific creatives (painters/composers) do a routine of between 1.5 and 3 hour sessions, one or two sessions per day. Depending on the person, but very consistent once the person figures out their routine.

That means 1.5 - 6 hours total. But this doesn’t include meetings and correspondence and all that jazz.

I like to wake early, work a bunch, then take time in the afternoon to do non work stuff.

Then I can come back at the end of the day and do another few hours. This lets me experience the world when things are less crowded, make time for family etc, while still having plenty of time for work.