I tend not to promote anyone to the bigs until they have to be on the 40(4th pro season).
I have a RL/LoA/HiA, AA and AAA "schedule" where they play a season or at least the majority of a season at each of those "levels". So, by season 4, they've played a good bit in AAA.
However, a player will not suffer in development if he plays full-time at the BL level. He just starts his arb/FA clock earlier.