iahphx "Earlier, I linked to the official info site. You have to arrive by a fixed time, and, I believe, leave by a fixed time. They have gates and will certainly close them. I don't think you'll be allowed to head out at 10 pm."
I found the website maintained by the county and the phone info. It says:The viewing area is open daily from 5:00 p.m. until 10:00 p.m., as long as conditions remain safe for the public. The last vehicles are allowed in at 8:00 to allow people adequate time to view the lava before the site closes at 10:00 p.m. "
Thanks for the tip. My terribly short trip will be more efficient thanks to the flyertalk members' posts.
I'll post after my trip.