The decorations are usually all in place by Thanksgiving weekend. They usually come down a few days after NY's. Each resort has decorations that correspond with the resort theme.
Suggestions:
FW - One evening go and take the hayride or the campfire program. The campers go all out the closer it gets to xmas day. You will find lights, animated characters and music on many of the sights.
GF - A huge gingerbread house in the lobby that serves as a gingerbread store, a gingerbread carosel and xmas music that starts in the afternoon and goes into the evening