Before Christmas/After New Year's
I know last year when a friend of mine went on Christmas Day and the day after they had to suspend ticket sales and entrance into the park for a while because it was at capacity. Pretty sure my friend had said that on Christmas Day it took nearly two hours before they started letting people back into both parks. To be honest that's the first time I have ever heard of that happening and thought she was just making it up until I watched the news later that night and they showed clips from Disneyland about how packed it was during the day. Really want to avoid going on an overcrowded day if it's possible at all during those dates.