Usually the first week (or possible the first weekend and days after that) of December has the Candlelight Processional (which brings BIG crowds to DL, Main Street specifically I believe), and 2 nights of DL closing early for the Cast Member parties (DCA stays open later on those 2 nights).
CP was on Dec 1 and 2 last year, I think, and the CM parties were shortly after that, and we had a trip from the 5th to 9th and it was great. All the decorations and displays, none of the huge crowds that would be there in a couple weeks. But I think the weekend is "later" in the beginning of December this year, so it's possible those events will be later, and a 5-9th trip woudln't work as well this year.