May 5 is the day of the big media event at Epcot, with the park closing to guests at 3pm

There will be the grand opening for all the big-wigs, TV cameras, note-takers, etc, and all the media will then get to ride it for the next few hours. It will then be fully open to all on a regular basis May 6. However, it seems there have been 'soft' openings of the ride for several weeks now, as is usually the way, so the chances are you will still get to ride it at least a week before May 5. On a different note, the whole of Disney will be VERY busy with the media event May 4-6, and I would advise avoiding MGM on the 4th, ALL the parks on the 5th (with Epcot closing early and other events at MK, there will be more people crammed into less space than usual), and Animal Kingdom on the 6th.