With T5 lighting, pretty much the standard is 10-12 hrs actinic, 8-10 hrs daylights.
My actinics come on at 9:00 am, daylights at 10:00....daylights off at 8:00, actinics off at 9:00pm. Some people run a little shorter photoperiod, but I like to give my corals a nice full day of daylight. I also have it shifted towards the latter part of the day, so I get to see more of my tank at night, when I'm home.
People with metal halides or LED
's run less photoperiod too, because of the strength of the lights.