Lights on for how long ?

[George]

First of all, when you are cycling your tank, you don't need any light at all. After your tank cycled, you can turn run you PC lights for 10-12 hours a day. use a timer to turn on and off to match your schedule so you can enjoy your tank. As soon as you get your MH lights, you can turn on the MH lights for 6 hours a day.
I had an accident where my MH lights were on the whole night because of a stuck timer. My corals and fish didn't seem to be affected by it.