Back when hosting was a hobby, I worked a few hours a day on the hosting. Meanwhile I had a job as a tech for New Hartford CSD.
Currently, I still have that job at New Hartford, and own HostMyThing.com. Total time commitment per week for HMT, probably between 20-50 hours, depending on the week. Some days are busy, and others nice and quiet. I offer 24x7x365 support, and there are those days where I am up at 3 AM because somebody lost their password :/.
All in good fun. You gotta like what you do, especially in this industry. I can't imagine myself putting this kind of time in if I was just interested in the money.