It's really a hit or miss, depending on the time of year, etc. We usually have good luck with the earlier hours at MK, but we have never gotten there exactly at opening. There was not much for us to do at EP late night, as we're not into thrill rides, and there didn't seem to be many other rides open. We tried MGM late night twice on our last trip in Oct '05. One night (beginning of the trip) was very crowded, so we only did TGMR and left. I think that one ride took almost two hours to get through, including the line. The second time (last evening of our trip) we got to do every ride we wanted, with little wait. It was just me and DD12 taking advantage of it, and it was a really nice bonding experience. If I remember correctly, we did TGMR, Star Tours, Muppets, and Mermaid in a matter of a couple hours.