Early in the morning when it is still cool.
Evenings can be very beautiful. There is a gate on the West Side, but it will open to let you out if you stay to see the stars.
Hiking is better early in the day. And if you don't have a campground reservation, they have first-come, first-served sites. If you want one you need to be there as soon as the office opens at 9.
September is OK, best in the morning light.
Early morning or mid afternoon. Some shade in the afternoon. No shade in the morning but cooler.
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