Until reports from the first few days come in, it's hard to know how to time out arrival for an 8am entry to SW:GE. My fear is that I'll arrive early, but not early enough, which will lead to bottlenecks that'll mean I can't actually get into SW:GE until after the reservation time, which would obviously cut down on my 4 hour block. Here's my thought process...
Time to park car. Usually not bad first thing in the AM (at least at M&F) but expecting more people than usual showing up so this could back up at the toll booths. I forget, will the new structure be open by then?
Time at security. Again, usually not too bad early in the AM at the lot or on the DTD/DLH side for EMH. But it can back up pretty fast once people start streaming in from PPH and DLH. We know the hotels are sold out the first few days, so this could be a big bottleneck.
Time at main gate. Another big bottleneck opportunity. I assume that they'll let people into Main Street before the 8am opening as usual, and I hope that they actually start letting people in extra early, say 7:30 or even 7am just to get the crowd flow in order.
Time at rope. Unclear how this will work. They could hold people for normal rope drop at 8am, but that would mean a mad dash to SW:GE entrance. I'm actually assuming they'll have some kind of dedicated line in place for SW:GE that you can get in as soon as you are through main gate.
Time waiting to get into SW:GE. How soon will they start processing people and letting them into the land? If it is at 8am, which I would expect, only the first few people in line will actually get their full 4 hour block. It shouldn't take too long (I hope) to scan reservation codes, but if it's like waiting at the main gate, it could easily be 15 minutes.
Other questions & thoughts:
A lot depends on how many people are in each reservation block. Hundreds? Thousands? Smuggler's Run can supposedly handle 1800 per hour, so that's 7200 in 4 hours operating at maximum efficiency. It doesn't make sense that they'd let in more people than could actually experience the ride, or to expect the ride to operate at 100% efficiency all day. You have to assume there are some people who will go into SW:GE but not ride, but that's probably not too many people.
Will the line be too long to attempt multiple rides in the 4 hour block? If you just wanted to ride and not do anything else, how many times do you think you could ride? Once? Twice? More? Haven't seen anything to suggest you are limited to one ride.
Will you be able to stay in line if your reservation time has expired? This is for shops and especially the ride. If you've waited in line for an hour (to ride, or for a lightsaber, or some weird milk) it doesn't seem right to kick people out. If you can stay in line, then I'd try to ride Smuggler's Run first thing, then do other stuff with the rest of my time, and then hop back in Smuggler's Run line just before my reservation expires.
Will they use all 3 entrances (Fantasyland, Big Thunder, Critter Country)? Using all three entrances would speed up the entry process and distribute the crowd.