Hi!
since starting HRT I also noticed that some bald spots on my hairline started growing again. The new hairs, however, aren't getting too long. I think they grow quite weak, but after a new cycle they'll eventually grow stronger and longer. I don't expect the new hairs to be as long or as strong as they were one day.
One thing that I use daily and that probably helped me too is a lotion of minoxidil! It works shortnening the cycles and inducing the new grown hair to fall and a new stronger one to grow in its place.