Correct me if I am wrong (and I am sure someone will ) but I think it is the second weekend in Nov every year.
That said, please be aware that we were there during that time last year and the place was mobbed. They ended up closing the gates at MGM both days on the weekend. We had no intention of going, which is a good thing!
Mouseplanet is reporting that it is in october this year. It was in November the last couple of years and I think it was too busy the weekends they had it. I could be wrong but that is the early report that I saw.