Usually, on mornings where there is an EMH/MM, the first breakfast seating is about 10 minutes after EMH/MM starts and on non-EMH/MM mornings, the first breakfast seating is about 20 minutes before the park opens (this is often when they open the turnstiles to everyone and hold guests on Main Street). So based on your reservation time (8:10 am), I would guess that means the park opens to general public at 9:00 am, but there is EMH/MM from 8:00 am to 9:00 am on that day.