I have a few friends that went to Disneyland 50th. While this is a little different since you are guaranteed entry with the park res system, some things still remain the same. Disneyland had people lining up at midnight the night prior to the 50th. I had some friends get there around 3 am. Even though they arrived at 3 am, merch lines (I'm talking about DL had merch that was only for that day) were still 3+ hours. I had one friend wait 5 hours for merch. Not only that but the ceremony, let's say the gates open at 730am with a line already formed you might be waiting for 1 hour+ to get in. By that time the ceremony will be over.
Also, who cares. The 50th only happens once. I would rather get there around 6 am to catch the ceremony while my wife who wants merch gets in line for that vs getting there when the busses arrive and testing that mess. Even to catch the first bus you better be down there 1 hour before it picks up to even have a shot at getting on the first bus, so that's already 6 am that you would have to be ready by. Or you can wake up around the same time 5:30am, and instead of catching a bus you can pay the $15 for an uber to the contemporary and get there before the busses.