There are a few entry/exit gates that have regulations posted, and they say 7AM - 7PM. I've been on it at 5AM-5:30AM at times of the year when the first light of dawn starts peaking over the horizon with no issues, and a lot of others are out there at that time, too. I've been on it in the evening after sunset for short stretches and seen quite a few folks using it for workouts or as an off-street transportation route. I don't think I'd regularly ride on it at night due to the low visibility factor and the possibility of having a collision; there's a few areas where gang activity might be a problem, but that's secondary compared to the possibility of a collision. I've never heard of anyone being cited for using it at night.