May 22nd is the Thursday before Memorial Day weekend. June 14th is the first day that the majority of schools in the United States will be on break for summer. (Yes, I know many go on summer break in late May.)
The opening of Diagon Alley will happen as soon as all of the pieces are in order. They're not going to let it sit unused in a finished state for a few months to exclude a few promotional tickets or value passholders. Most park operators in the United States will tell you that they like to have their new attractions open and fully operational by at least Memorial Day weekend. I'm certain that Universal would agree with that approach.
Ultimately, the final phases of construction will determine when the opening actually occurs.
This project has moved along quite quickly, can't wait to see the finished project.
What we're trying to determine is what the deadline is on those contracts. Universal's promotion and blockout schedules, also determined far in advance, provide clues. Let's remember that this year's USF blockout sked blocked out the month of July, which led many of us to suggest that Transformers would open in late June, which it did. If I remember correctly, the previous year's calendar didn't block out USF in the summer at all. This year's calendar moves up the blockout by more than two weeks, into early June. That's not just a seasonal adjustment.