We were at WDW this January 5-11th. Christmas decorations were still up at all of the resorts we saw/stayed at - AKL, Poly, GF, YC, CR. We didn't get to the WL until the 11th, and the decorations were already gone there. We saw the Osbourne Lights on the last night - Jan.6th - it was really crowded. Also there were still some decorations up in the parks while we were there.
Hope this helps-