There are no restrictions on the time into the park. No locked gate etc. They just hit you to pay on the way out.

You have a 7%+ section right at the end. It isn't that long but it's steep. I'd really be wanting a 32 there or a MTB triple.

HWY 62 from what all the locals have told me is definitively NOT recommended for riding so I wouldn't consider a loop. Since you have SAG a thru the park starting at the West entrance and up to Keys View would be fun. With support I'd do that rather than an out and back. You will see more of the park that way

It's about a 2.000 ft climb out of the town of J Tree into the central part of the park. then most of it is relatively flat. Once you cross Sheep pass it's pretty much all down hill to 29.

European tourists flock here to experience the desert, so expect rental RV traffic even mid summer, although they seem to be a bit more attentive than the domestic retirees that dominate the RV traffic in the winter.

WFIW

I've only ridden there a few times, up to Keys View from Boy Scout one of them, but I've been climbing there for 45 years and have the topography committed to memory.