Mine come on when my photo period ends. I don't know if there's any validity to my worry, but the room my tank is in is VERY dark at night. I have a large green carpet anemone, and have always figured a little light might help some of the other critters to not mistakenly "blunder" into it in the dark...

I do a 12 actinic and 12 moon with 8 hours of MH during the actinics. I also stagger the 2x250W MH by 2 hours so there's a "high noon" period for about 4 hours. I use a Neptune to control it...

So the Actinics come on at 9:00AM and off at 9:00PM. The moons come on at 9:00PM and off at 9:00AM. 1 actinic comes on at 11:00 AM and off at 5:00 PM. The other actinic comes on at 1:00PM and off at 7:00PM.

I works quite well I think...