I might be wrong...or it might have changed by now...but if you stay on grounds, I think those people can get into the parks 1 hr before it opens to the general public and 1 hr after it closes to the general public. We had some friends stay there a couple of years ago.

When we were there last (about 8-10 years ago), we stayed off grounds. When we go back (hopefully spring '07) we are going to check into staying right on grounds. That way if we want make sure we're fresh for the fireworks at night, we can go back to the room/pool and hang out there for awhile and come back when we're ready. That's not so convenient if you stay off grounds.