Comment by gus_massa

Thanks for the reply. There are a few claiming 12 hours per day, but it looks like it depends on the site.

Sorry for the delay, I wanted to write a long reply about my experience in math/physics. Short version:

After teaching math for 3 hours I get tired, and in some special cases I teach for 6 hours but at the 5 hours mark I was making too many errors. (And it included some pauses in between.) I'd would not try to make a decisions that risk lives after that.

I took some exams that were 3, 5 or even 8 hours long. It's possible but I have to administer the pauses, bathroom and even going to the bar to drink a coffee to survive them and give good answers. And in case of a mistake, I can review it half an hour later and there are no lives at risk.