Here are some sites that I think will provide that information.
http://www.google.com/search?hl=en&ie=ISO-8859-1&q=area+51+and+9-11-2001+&btnG=Google+Search
what year will the government release all the files or whatever about area 51 and 9-11-2001
3 answers
what day will the archives relaese the info like i heard in 2049
I didn't find any specific date. However, if you carefully read the sites posted by GuruBlue, you may be able to find that information.