I've found that if I've forgotten to take my estrogen for a dose, my breasts start hurting the next day, and then I take the hrt and they seem to grow. I'm not sure why, or why it seems to kind of trigger a growth period.
Now that I'm post-op, the affect is a little more and they've been hurting lots. When I stopped hrt for surgery, they hurt after and continued to grow for two weeks. After surgery and after starting HRT they seemed to not grow much at all. After a few months, they started up again and so did my whole body and tons of changes. I think during the first couple of months my body was busy healing more so than trying to grow breasts. Now they are growing fine.