I know they are always up by Thanksgiving (official start of holiday period) but as with the Halloween decorations, they start appearing before the official start. This year the week before the official start of Halloweentime the decorations started appearing. The giant Mickey on Main St. was up the day before they said and HM holiday overlay was also open on Sept. 25 (thursday) instead of Friday the 26th.
I just checked the website and the Christmas Fantasy Parade starts on Friday, Nov. 21st. so the decorations should all be up by then and maybe even earlier.
I'm happy to see that the parade is starting on the 21st since my Nephew18 finally got hired by Disney and is a reindeer in the parade! Since this year we got the SC Select AP and we can't go on weekends or from 12/19 to 1/4 we'll have almost a month to go see him before we are blacked out.