I've only had to do it the night before once but because I foiled the butts,I poured all the juice from the pork into a bowl and put it in the fridge,this helps the fat rise to the top and solidify makeing it easier to remove. Heat the reamaing juice in a pan with some of the rub you used for your cook and warm it up then pour it over the pulled meat and mix. I used two large foil pans for the meat so I just covered them with foil and tossed them in the fridge, the next day about an hour before it was going to be eaten I warmed the pans in a 250 degree oven,sprayed it again with a little vinegar and mixed again