Sorry to hear of the bad weather and change of plans.
So you have entered a kind of weird Food Safety area. You are essentially reheating your pork. You will want to go from <40 to >165 in <2hrs. After the 2hrs you can turn the oven down and allow time and heat to do its thing. Here is how I would do mine:
Put some liquid in the pan (beer, apple juice concentrate and diced onions)
Wrap with plastic wrap then foil. (the plastic wrap protects the meat from the reaction the foil has to the acids in it, as long as the plastic is covered by the foil it will not melt. Do not exceed 350 oven temp)
Place in preheated oven at 325 degrees
After an hour check the internal temp. If it is still below 120 you may want to consider cutting the butt into smaller pieces to allow for faster reheating.
Once you have reached the 165 degree internal temp mark. Turn the oven down to 275-300 and allow to cook till 195-200 degrees internal temp is reached.
Remove from oven and allow to rest for about 30 min, then pull.
Save the juices in the pan for your finishing sauce after you pull the pork.
Hope this helps. If I left anything open just ask.