Great question, have thought about this myself. Here are my thoughts:
First, it is probably more like 60 minutes you are splitting between the 3 because Terry not Dooling will be Rondo's primary back-up at point guard. So throw in 10 minutes at the 1, and then another 2 per game for small ball when Lee at 6"5 plays the 3. Give or take.
Assuming 60 minutes, I would say you have Bradley playing 28, Terry playing 20, and Lee getting 12 minutes a night.
This is also assuming Avery Bradley is playing at the level he was playing at last spring, which I am not completely sold on.