This is just my opinion. Went to US last spring - were there 2 1/2 days - but really 2 days with EXPRESS PASS is sufficient (and we didn't stay late - left around dinner time 2 days and 11 am the last day)
Early Entry: Do early entry and hit whatever HP side is open FIRST. Do NOT go to minions or otherwise get distracted - EYES FORWARD. Head straight for either Gringots or Forbidden. Have your fastest "walker" get there and pop any bags into the lockers (free and convenient). REMEMBER YOUR LOCKER NUMBER and COMBO. Rest of party gets in line - bag person meets up.
Once done - if the line isn't bad - hit that ride again (you will want to - both rides are just awesome!!
Stay around in HP for as long as you like. Then start tackling the rides you want. We did MIB 4 times in a row as we all had fun on it. And we just made our way around the park. NO PLANNING - can you image?!?!
If you are a HP fan - get into Olivander's early as the line gets long for the "ceremony". It is fun and the "actors" really get into it. I liked the one on the Diagon Alley side best.
But once in the general area of the park - just do what you like as many times as you like. Even with EPass there are some rides that have some wait (Rip Ride Rocket /Minions) however it is ok. On IOA side there are about 3 or 4 rides where you get wet - well not so much wet - but soaked. We saved all of them for the same day in the afternoon just before we wanted to go back to the hotel. They have dryers that you can use - but there is a line, they are expensive and you still have soggy shorts - so just group these rides and do them before you leave - unless you like soggy shorts (I don't judge).
I do also suggest MYTHOS to eat. It is just outside the Hogmead's are of HP on IOA side. It is nice and quite and cool. The food is marginally more expensive than a counter service - but it is just a lot nicer. The food itself was actually quite good.
Also don't be afraid to go back and forth on Hogwart's express. We rode it one way - got back on and rode it back. You MUST have a HOPPER PASS though.
The really nice thing with EXPass is you DON't need to plan.
Hope this helps