The National Parks released the holiday hours for September this year.
In general, there will be shorter hours Wed Sept 4, the eve of Rosh HaShana (parks will close at 1 pm); the Friday Sept 13, the eve of Yom Kippur (parks close at 1 pm); Wed., Sept 18, the eve of Sukkot (parks close at 4 pm)
Saturday, Sept 14 - Yom Kippur - all parks (and just about everything else) will be closed.
Keep in mind that the last entrance to parks is always an hour before closing time.
All parks will continue with a summer schedule until Oct. 27.