I can't speak for the party - but, if you are doing other parks during the day - including MK - most have Santa appearing. I think MK has him closer to Christmas but when we went last year we saw him at Epcot before our seasonal passes blacked out (meaning not too close to Christmas) and we only waited like 10 mins. He was with Mrs. Clause (in the American Pavilion) and one of the greatest I have ever seen. "Santa Goofy" is at Hollywood Studios and Santa can also be found at Downtown Disney as well.. so you have a number of options, I am sure as we get closer to the holidays some type of schedule will appear to give you a better idea of opportunities and if any will fit your needs.
Now, if you are only going to the party - you still have the option of DTD.. but again, I have no idea about lines for him AT the party.
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