First year commitment is at least 8-10 hours a day with one day off for me.
Figure on an even wash if you work 55 hours a week right now - not much will change. Second and third year supposedly takes less time studying, but more time on other stuff (moot court, law review, memo's, research, panels, externships, etc).
Treat it like a job and you'll do fine. Treat it like a return to undergrad and you will have major problems. Each week is a little different, especially when PRof's change things up. I've never had to put more than 55-60 hours in yet and I'm doing just fine (actually, I'm ahead).