Usually it's within two weeks. I'm pretty sure the letter with all of the board dates sent out a while back also has the expected release dates.
You can keep a tab on the scholarship checker at afrotc.com to see your status when it's updated, or even the DoDMERB website (you'll be able to register an account if you were awarded a scholarship).
I don't think there's a specific number, but unfortunately it seems to be lower than in the past based on recent boards.