Everything should be open in September before the winter weather is on its way - a great time to visit after the summer heat and crowds.
The museum and visitor center is open 8 am - 6 pm until October 31st. The park grounds are open until 10pm. You can find all this info and buy tickets at www.nps.gov/gett ... It's a great time with tons to do! I highly recommend the car tour which is two hours of a guide driving your car packed with information.
The park is open daily, but each center has different hours during different seasons. September is a great time to go and everything is open.
Thanks! Your answer is awaiting moderation.