Disney have a tradition of changing over their seasonal decorations in quick time. The bulk of the change from Halloween decorations to the Christmas season take place over night after the final Mickey’s Not So Scary Halloween Party on 31st October before the park opens the next morning
Disney published this time lapse video of how it is done a few years ago
I haven’t visited the park at this time but I have arrive just a couple of days after and the park was fully transformed.
