As a rule of thumb, the tourney will likely end when there are 20 big blinds in play. For example, if you have 15 players, 5 rebuys, and T20,000 starting stacks, that would be 400,000 total in play. The tourney will likely end when the blinds are 10,000/20,000.
I think average blind increases of about1.5x is best. Adjust your level times, or starting stack sizes to match your time goal.