They dont typically have to close the park due to capacity. Its most common right around Christmas- This year I would say Dec.22- Jan 1 are going to be the busiest days of the season. Earlier in the month will be a little quieter. You'll be able to tell what kind of crowds to expect when the schedule is posted. If they are open the max hours (8am-12am) then you can expect things to be busy. The shorter hours indicate smaller crowds. The first full weekend in Dec is typically candlelight pro. and will be busier then the days leading up to and following it.