Never had it close early, but have had days randomly in the middle of the week where they do not open. Never went to Mountain Creek, but various Poconos areas in PA. (Blue, Bear Creek, etc.).
Unlike out west, the resorts out here just don't get much volume in the weekdays. Hence, the discounts, unlike out west. Most of the customers in the east are locals, not tourists on a week vacation.
However, this generally happens really early or really late in the season, mostly to save whatever is left of the snowpack.