Holiday decorations will be up in New Orleans Square and snow on the Castle before Halloween. Then Main Street is decorated super-fast as they will probably tape the Christmas Parade Nov 2-3 (although it is possible they may push it back a week to Nov 9-10). The Tree is installed at Town Square and Christmas opens at the resort Monday Nov 11th (but if they push back the taping of the parade, Christmas will begin later, perhaps Wed Nov 13th or Friday Nov 15th).
Best bet: Wait to book until the refurbishment schedule is announced for Fall. The day Small World comes out of its closure to install the Holiday overlay is the day Christmas starts at the resort.