Go for 10-12 hours on. If the room is not sunny, I'd set them when you're home most (i.e., if you do nights, turn them on 11am to 11pm). If the room is sunny that might stress out fish with too much light, so you'll have to somewhat match daylight.
55g reef, 2x250W 10k MH
+ 2x96W PC
actninc, 10g sump, AquaC Urchin skimmer, 65lbs LR
xenia, mushrooms, wels. open brain, fungia radiata (orange), green eyed zoos
flame angel, mated pair of false perc, 6-line, firefish
20gH electric yellow cichlid