I'm not 100% certain what the deal is, but in all of the ads I've seen and on IMDB, the official release date of Star Trek is May 8th (Friday). However, many theaters are showing it on the 7th at normal times (I'm going to see it at 8PM). Why the odd timing? I suspect that what's going on is the movie studios coming to terms with the midnight showing phenomenon. To date it's been a fairly standard practice that for highly anticipated movies, the theaters will have a showing at one or two minutes past midnight on the night/morning before the release. Because technically this is still on the correct day, they are obeying the terms of their contract, but it's harder to get the right kinds of media buzz going at 1AM than it is at 8PM.
The end result is a wide release on the announced date with "select theaters" (I'm sure there's a lot of negotiating over what it takes to be "select") showing it on the day before.
Anyway, this lead to my selecting an 8PM showing tomorrow night, and while I'm very excited, I have to say that I'm a little scared. For over a decade I've wanted Paramount to clean house, get rid of the old guard that had turned Star Trek into the Vulcan Oiling Show and do another movie with a sense of purpose. Now it looks like that's what we might have, and my enjoyment of Star Trek is at a cusp. Either I'll come out of this film eager for the next in the franchise, or I'll likely be done with it... we shall see.