Pat, how did you normally pace yourself before? If the hour thing works for you, that's great, but I've never been able to time myself, and would feel awkward working on a timed basis. If you're in a "groove", would you give yourself a few extra minutes? Or if you're in a fustrating spot, would you force yourself to work thru it? I've had times where I could work hours at a time without breaks and other times where multiple breaks were needed!
I need to do more color also, but am in a similar situation as Jeff. Pastels leaves dust, so I can only work in my attic which is freezing during the winter. I plan to do color later in the year when it gets warmer. Two classes a week?, lucky you. The only day I have to take a drawing class, my daughter has a tennis class at the same time. Maybe she'll make millions at it, and let her old man retire.