All mine are on times 9am - 11pm maybe my fish get ticked at me for making them stay up so long??? but I can always tell when its lights out time, the fish will stop their normal round abouts and start hanging out in their normal sleeping area. My pleco tank the lights are just randomly on mainly when I am trying to see them I would say it depends week to week but normally only one once a week for 8 to 10 hours, that tank has lights of 98% of the time. I once thought about setting dim lights for the first 2 hours and the last 2 hours and bright the rest of the time to simulate rising and setting but decided it was not worth the hassle.
There was a fish store by me that for a while had HID lights on a motorized track above a large reef, I guess it was supposed to move and more accurately simulate lighting?