We were there the first week of January this year and most of the decorations stayed up until around the 7th or 8th. We got there on the 1st and still got to see the Gingerbread house at the GF and the chocolate display at CR and the Chocolate Poly. On about the 4th or 5th the Christmas tree in front of the CR came down and we got to watch the cranes take it apart. They do start coming down after the 1st but, there are a lot of them and it takes more than just a couple of days. If you get there during the first week, you have a good chance at seeing some of the things!!
BTW, it was a great week to be there and we may be going back that week next year too!