To the right hand side there are turnstiles for ADR guests. You will probably get in a little early if the park does not have morning EMH that day and opens at 9 am. I would guess they will let you in from around 8.50 onwards for your 9.15 reservation, but it all depends who is manning those turnstiles that day. Since Disney asks you to check in 15 - 20 minutes early for your ADR I don't think you will have a problem.