DHS also puts Christmas decorations up right after Halloween, and you will hear Xmas music playing in the park in early November.
We did both parties in 2012. The last Halloween party was 11/2, and the first Xmas party was 11/9. We had already planned to 11/9 Xmas party as part of our itinerary, while 11/2 was our arrival day. Once we realized it was a party night, we moved our flight to earlier in the day, and did the Halloween party, too!
As stated previously, this year the spread is 8 days (instead of the 7 days in 2012), so still definitely doable!