12 on 12 off is good. Mine get a few fishroom lights & light from a window during the day, it's sort of a half light thing. I'll turn on the room lights after work, they sometimes don't go off until late, 11 or 12, depends what I'm doing in there.
Fry tanks get light 24/7 for the first couple of weeks. This keeps them from settling on the bottom where bacteria tend to congegrate.