I would think it would depend on the circumstances. Checking in every hour during a movie would be a little disruptive, for instance.
Does he have a cell phone to use? Otherwise he'll have to make sure he's by a phone every hour.
I was brought up (by my mother) to be very considerate with regards to where I was etc. I'd call her after school if I wasn't going straight home or to her office. I had to let her know where I was going and who I would be with, and how long I would be. If I was going to be any later than that (for whatever reason) I had to call and let her know.
Hmm, actually I still do all those things! Whether its with my mom or my fiance! Guess I've just incorporated it as courtesy.
I would think that every hour might be a little much. What about every 2 hours? Gives him a little more freedom but still the responsibilty, without him feeling like he's chained to a phone or being watched long distance.