Are there park rangers during just the day or also at night on campground sites?

They won't bother you unless you're walking around with alcohol or your parked in the dirt or some kids riding around without a helmet

I believe the guard shack closes at 9pm but there are camp hosts living year round in each campground.

Day and night

they're there during the day; but really stay out of your way. The camp hosts watch the beach at night...again, only see them if someone is misbehaving.

24-7 great for family's!