Steve -
the BAHA surgery is totally different from the AN surgery.
It's much shorter, done on an outpatient basis (you can even elect to have local anesthesia), and they don't open up your head. It's similar to being scalped - sorry, that's how someone described it to me and although the description is a little unsettling, it's true. The site is only about 2.5 " x 2.5 " though - so don't picture yourself completely scalped. You don't have the recovery issues of AN surgery either - balance, dizziness, tiredness, etc.
I had my BAHA surgery 9 months after my AN surgery - would have had it a lot sooner, but my insurance company was not cooperating - and my head was still a little numb. It was actually a good thing because I didn't feel the doc injecting the lidocaine into my head
I don't think it's too soon - but I'm an accountant so my opinion on this doesn't count - better ask your doc
Jan