Second BBL. How long should I wait until I have a second procedure?

It looks like you have had quite a change. I would give it about 6 months before considering any sort of additional BBL procedure.

Based on one photo it isn't easy to say what happened exactly, but you do have some dimpled lower skin that could be tight.  As long as you have enough fat, a secondary procedure prioritizing the fat placement into your preferred areas is a good idea.  Now that you are more than 6 months out fro...

Ideal candidates are at a stable weight,  in good health , and have excess fat in some parts of the body and too little in other regions.  Gaining weight before the procedure is to no advantage and when you lose weight again the fat cells will shrink just like the donor site fat cells.  ...