2 months post-op forehead reduction. How long should I wait to get a hair transplant?

I had forehead reduction two months ago, my scar is healing. But my forehead is square, I want to correct my hairline with hair transplant. So how long should I wait to get a hair transplant after forehead reduction? 4 months is enough? The hair transplant surgeon tells me that given my scar, 4 months is enough. What is the risk of doing it too soon?