I think it will be open in June, but they may still be working a few kinks out.
I've got a friend who is working on this project who said they were told to have everything up and running before the Grand Opening/Memorial Day. That's not to say the Grand Opening is Memorial Day. This person wasn't allowed to tell me what date that would be as that's very hush hush still.
My guess is that it will be sometime between May 21st and 29th. We know that several of the actors have said they are coming in May, and one even said late May (though I can't remember which one). Also, the Universal hotels were blacked out for the weekend of the 21st for a while, suggesting that a large event was taking place where they would need to ensure they had enough rooms for the events guests, and a grand opening with lots of rooms for press, celebs, and contest winners would fit that bill the best. In addition, the contest sponsored by the Today show for a class of school kids to get to go to the opening states that the winners will be selected April 23rd - 29th, and then will have about 25 days to make their travel arrangements. This would have them going to Universal during that magic week I've just stated.
Thank you for this analysis, MadeToLove! I'm hoping it's Memorial Day weekend or later. I'm checking on this every day so that I can change my hotel reservations to the correct date, and I certainly hope that the Universal hotels don't have the grand opening time blocked out. That would not be good!

Hopefully, they'll make the announcement soon, and then the daily-watchers like me can jump on the hotel reservations pronto. Here's me checking constantly:

I'm keeping my fingers crossed for all of us hopeful-grand-opening-attendees! Here's me cheering us on:
