We had 8:05 reservations for CP, and the park didn't open until 9:00.
We had no problems getting in; we just had to tell them we had a reservation.
If I were you, I would try for a little bit earlier reservation, then you could get into MK early and take pictures with very view people in the background. Either way, I would try to get in before rope drop, that way you don't have to deal with the mob.