We normally go to WDW during Jersey Week. It is the the same week as Election Day. This year we will be there 11/3-11/10. Sometimes, by the end of our trip they are starting to put up decorations, but I don't think they finish till about Thanksgiving Week.
Sorry, I couldn't give you a more definite answer.
It takes Disney about a month to get completely decorated for the holidays. First priority will be MK, since the MVMCP start in mid-November. But you will start to see decorations going up beginning November 1, and by Thanksgiving, everything is in place. Most of the holiday entertainment doesn't start until Thanksgiving, with the exception of MVMCP.