Around 7pm the sun goes behind the Western hillside... Around 8 it's a good idea to grab a flashlight. I should also mention that's on a clear sky day...
I've gotten into a camp site early as long as it is vacated and the camp host has gone thru the site and made sure it's ready for the next guest.
I'm not sure about when it gets dark but you can check in early if the space is vacant. Otherwise you have to wait until the other campers checkout which is 12 I believe.
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