Yes - my strategy for crowd avoidance, but still enjoying the lower-crowd morning times is to usually show up at the gates right around the posted opening time. When I arrive, no one is standing outside the entrances any more, and I've missed the initial flood of people into the parks, so they must have been let in a bit early. The "real" rope droppers will come along, I'm sure, and can give you park specifics on how early and what usually happens.