We arrived for early entry both Monday and Tuesday around 7:10. I wouldn't plan to arrive much later than that. In fact, I'd suggest by 7. Throngs keypt developing after that. One morning we got off by 8:45, and the other, we stepped off around 8:20. After, we enjoyed Diagon Alley (very empty) until around 9. It's spectacular. We spent a large portion of three days there.
As for the rest of the park - stay away from the Minions and Shrek after lunch. Both, we waited over 40 minutes - even with the Express passes. Both were not great.
In fact, the middle of the day, I'd stay away from everything with any wait. After dinner, we FLEW through the lines.
We had three days.
First day, Forbidden Journey at open.
Second, Gringotts.
Third, Gringotts.
Both days, the ride had significant backup and issues. The 'elevators' were completely broken the first day - one was just open to walk from one side to the other.
The second day, one was working. We stepped in, and it simulated going down into the depths. Cool idea. But was sorta wrecked by the previous day. Both days had significant breakdowns. Worth the wait. Fun.
But Diagon Alley is breathtaking.