The current rumor (and I stress that it's only rumor!) is looking for an official opening around 16 Sept. This is due to a planned internal party there to coincide with a certain Mexican holiday (I don't know which one, so I don't want to guess).
Beyond that, the Disney people have said that they plan to have it opened before F&W which starts 1 Oct, so that 16 Sept date fits. Of course, it's all rumor and guesswork at this point.
As posted above, once the official opening date(s) have been set, then we're likely to hear about reservations at that time.