Right now it is scheduled to reopen on June 19th. However, another 'Dis'er actually works on the RR at Disney and has told me that the new station is a pre-fab and may go up easier than expected. If that's the case it could reopen a bit earlier. Although, I guess the opposite could be true and it could be pushed back. Either way, the official answer to your question is June 19th.
HTH,
Rhonda