I've had an 8:05 ADR.
We arrived about 7:30 and after going through security we lined up at the gate. At approx. 7:45 the CM's started letting us into the park but kept us in the area just after the turnstyles. At approx. 7:45-7:55 (it sure felt longer) we were allowed to walk up Main St.
If you arrive after 8:00, I'm sure the CM's will allow you into the park when you arrive so you can get some photos of the castle before your ADR time.