We are early risers so getting to a park before opening is no big deal for us. We always get to EMH / regular RD early. I look at it like this:
We'll get to do a nice handful of rides with very short waits before starting the fastpass barrage, and generally, we're done with most of we want to do, including multiple rides on things we like, in time to depart during the hottest part of the day to go enjoy the pool that we're paying for. The downside is that we are generally toast by 10pm, but we don't mind it at all.
I think the longest we've ever waited for anything was:
Splash - 30 minutes (tech difficulties with a FP - I was hoping to get an anytime in
MDE so we stuck it out)
FOP - 25 minutes (I would wait 25 min again for FOP, and that's saying something.)
Speedway -20 minutes (early am when they were still bringing cars out. Grrrr - posted time was 10 min)
My best advice to you would be to get to EMH EARLY. If you get there 30 minutes into emh, I wouldn't bother.
Also, have a plan of attack for emh. Example: If you get to MK emh, but not early, some of the high demand stuff might already have lines not worth waiting in, but other lesser demand attractions might allow you to do them with NO waits, because people clamor to other things (like 7d?) AK is a good example as well. FOP might be a zoo, but you might be able to walk on EE 4x in a row if you'd like. BUT, if you get to AK an hour before EMH RD, you might be rewarded with a walk on fop + a Safari, (if it's open) + 3 EE's in a row, and then head down to Dinosaur after opening, and do multiple walk ons in a row before starting your fastpasses.
Early bird generally gets a worm. Other birds get worms as well. Decide which worm you'd like.
I'd be pretty confident in getting to do most of what I want without being an early bird, because I'm confident in my MDE-fu for fp hunting. The thing is, though, we're up early anyway, so getting to a park is not a big deal at all. And we LOVE the idea of chillin in the pool in the hottest parts of the day instead of crowd battling. For as much as we are paying for the hotel amenities, we're gonna try to get our money's worth.