Looking at my calendar from this past semester I was in 3 courses, which each met for 3 hours had 8-10 hours of homework each week. I attended 4 weekly seminars (1 of which I was helping organize; two of which I presented in some weeks). I taught one course which met for 4 hours, double that for class prep. I had 5 hours regularly scheduled in the tutoring center, plus an office hour. I’m slow at grading, so it often took me 4-6 hours per week. Plus an hour a week for my advising meeting, and we’re at 60 hours before I even begin talking about when I’m doing my own research - I typically try to devote my weekends and also Thursday afternoons in their entirety to either reading math books of interest to me or papers of interest to me (I do the rest of that stuff MTWF).
So it’s not quite 90 hours a week every week. There are weeks when the tutoring lab was shortstaffed so I needed to pick up an extra three hours there. There were times when I would proctor a 3-hour exam. There were lots of severe injuries in my department this semester so I’ve covered people’s classes too. So there were a lot of 90 hour work weeks just due to the structure of everything, but I guess saying that every week is a 90 hour week is an exaggeration. I don’t think I’ve worked fewer than 75-80 hours a week all semester though.
I only spend one hour a week in my office for my office hour.