I used to have a friend whose normal schedule was 10 hours per day, 6 days per week (and occasionally 5 hour half-days on Sundays). I always thought he spent way too much time at work.

That was nearly 40 years ago, and I've often matched his schedule for a few weeks at a time in the years since.

I think I worked 16 hour days X 7 days a week for six to eight weeks one time. I was pretty exhausted by the time that ended.