My home course is in a city park that's open until 10 PM. It's pretty deserted at that hour, but noone's ever giving me any trouble. Most of it's not very well lit, but once your eyes get adjusted it's not so hard if you know the course. I've bumped into a few other disc golfers out at night.
I did see a cop there once late in the evening, shining his light around in the bushes. Not really sure why - looking for kids? Maybe he lost a disc! Anyhow, it was well within park hours (which admittedly aren't well posted.)
They do occasionally lock the gate at night - and maybe sometimes before the official park closing. So, I have sometimes worried about my car.
I have played a few times on a university course without clearly marked hours, and wondered if they'd mind. One time, campus security was out shining lights, from their car, on certain fields that may have been part of the course. I was a ways off, and just sort of kept playing. I didn't go over and introduce myself, but neither did I hide. I was using glow discs with an LED, and maybe also a UV flashlight. I probably occasionally used a white flashlight. If he'd _wanted_ to find me, he wouldn't have had too much trouble - at least not if he had gotten out of his car.