The VIP party in Diagon Alley is the night of the 18th. The 19th during the day is when the press gets to hang out in DA. The 20th is scheduled as the departure day and press has to check out of their hotel in the morning, so it seems a strange day to stage a grand opening ceremony...
During Phase 1, they held the big grand opening event on the 16th with all the movie stars and the big fireworks show for all the press. Then the land officially opened on the 18th. So, following the schedule you mention, it seems like an total repeat. The night of the 18th will be the big "event", the 19th will be the big press day and then the 20th it will be officially open to the public. Even if the press has to check out of the hotels, it doesn't prevent them from going to the park opening day. However, they should have gotten all the video/photos they needed the day before. Honestly, having tons of press in the parks when it is open to the public will just cause more of a headache for everybody involved.
Plus, with the tonight show going down, they can film parts of the big, movie star filled "opening" on the 18th and then include it in the show on the evening on the 19th and officially announce to the public that it is now open.
Of course, this is still the most ideal situation. I am still standing firm behind the idea that you don't invite TONS of press to "preview" a land for a few days, send them home, and then two weeks later invite them ALL back down again for the opening. Also, Universal is not going to put into the press schedule "A star studded grand opening event" on the 18th considering they have not announced the grand opening date yet. Info gets leaked ALL THE TIME. Its better for Universal if they just call it a party on the schedule so if something does get leaked from the schedule (which it has), people won't assume it is the grand opening party.
You also don't start ramping up press coverage (including Universal's own press team) if you are not planning on opening it soon. In the span of eight days we had five stories regarding this expansion on the official blog alone! They simply can't keep releasing stories about the land every few days for another month. People will get frustrated that they keep showing off all these great details without being close to opening. It's the same logic all the entertainment industry follows. Release a trailer in the movie theater for a movie months in advance and then 2-4 weeks before opening, start the main press push with TV ad's, interviews with the cast on various websites, ticket pre-orders (for big movies), etc. Same thing with video games. Tomorrow is E3 were a LOT of new games will be shown off. They will have there big reveal and some gaming sites will cover the games more in depth but then all the names will vanish for months. Sure some people might remember them and talk about them daily (like us on this forum with HP), but the general public will have mostly forget. Then 2-4 weeks before the launch of the game, the press push begins with tons of gaming sites covering the game, interviewing the creators and then mostly ending with the games release by publishing the review (same goes with movies).
To me, Disney really screwed up with 7DMT. After the big press event, I was excited to check it out and wanted to go right away but it was still not open! A week later I had forgot the day it was even scheduled to open and then when it did official open, they had barely any press coverage because all the press had covered it a few weeks earlier.
