I've gone to WDW the very beginning of January the last 3 years, and it really seems to vary. One year, as I commented, the trees at POR and POFQ were still up when I checked out on 1/8. As CMs said, "We're running late this year". But if there's something you really want to see, see it ASAP. Once I went to Epcot the day I checked in, 1/2, and saw the tall tree, winter arch. Went back 2 days later and everything was removed.