If there is no work that needs to be done on Haunted Mansion beyond just the removal of the overlay (no refurbs, in other words), then it should take no longer than a couple of weeks to remove everything, at most. It was down by the 12th this past January, and I think it reopened in non-holiday form by January 26th or somewhere in that range. Generally, Disney tries to time it so that Haunted Mansion closes for the overlay removal first, and then when it reopens It's a Small World Holiday closes for its own overlay removal. That way, they aren't both down at the same time.