Are airport car rentals always open until the last flight has landed, regardless of the official working hours?

Recently I had a flight to Kona/Hawaii that arrived at 10pm. The local car rentals all appeared to close at 10:30pm and there’s now a secondary COVID test in Hawaii that can take up a lot of time, so I’ve decided I’ll just get a taxi and come back for the car the next day. But to my surprise, I saw a car rental shuttle at 10:45pm and was in fact able to pick up my car. Their employee told me that they’re always open until the last flight has landed and picked up their luggage, so their hours vary.

Is this the case for all airport car rentals, at least in the US? Can I always book a car without worrying about my flight being delayed?