That's not exactly "early" in the context of other late Sept non-party dates currently on the park calendar. The park calendar currently has 8pm closings for all non-party MK nights from mid-late Sept.
But, those hours will (in all likelihood) change around a month'ish out, so keep checking back. FWIW, park hours that same Saturday last year (just for reference, no guarantees for future results) were 8am-12am.