Well, they haven't released the dates on the English Grad Nite site, but they have on the Spanish Side... (So there might be a change or two)...

http://www.disneylandgradnite.com/as...pp_Spanish.pdf

Thursday, May 19th
Thursday, May 26th
Thursday, June 2nd
Thursday, June 9th
Wednesday, June 15th
Thursday, June 16th
Wednesday, June 22nd
Thursday, June 23rd.

So expect the park to close early on June 15th, 16th, 22nd and 23rd (more than likely either 8 or 9 PM).