If I buckle down I can do 10 hours a day 3 days a week for a few months, then I burn out four a while. If I do 4 to 6 hours a day of low to medium intensity work (focused debugging with interspersed Google searches and occasional HN breaks) 4 days a week, I’m able to keep it up forever. I don’t think I’ll ever be able to do 9-5x5 ever again, especially having to go into an office.