I generally do an hour lesson, unless we're just doing something really focused like jumps. I don't like feeling rushed when learning new physical skills, and it seems that 30 minutes is gone in a blink--unless we're doing back crossovers, then it's never-ending.
Practice depends on the type of session. Public is slower, and there are hockey players and toddlers running amok, so 1.5-2 hours works. A lot of my workout there is edges, moves, power pulls, slow stroking, turns, spins, and a handful of jumps.
Freestyle tends to get my heart pumping more, as everyone is skating a lot faster, and you need to KEEP MOVING. I use this for fast stroking exercises, program run throughs, and a lot more jumping. After an hour, I'm ready to beg for mercy.