Rehabs are rarely announced more than a few weeks before they begin. Rumors from CMs may begin to swirl about earlier than that, but there usually isn't much advance notice at all.
If an extensive closing occurs several months before your trip, obviously you'll know about that when it occurs. But if you're trying to check a rehab schedule before even making vacation plans, forget it. There's no way to predict what will happen in March, much less in December.
December does tend to be one of the lighter rehab periods as they are getting geared-up for the holiday crowds. But no guarantees.