| I am assuming that this is a SW tank?
If so, I am not the expert and still learning myself, however I do know that allowing too much light in a tank can lead to algea problems and should be considered. For my SW tank, I use timers to turn on the blue actynic lights approx one and a half hours before my white lights in the morning and then the white lights turn off about two hours before the blue actynic lights go off at night time. I do this to simulate dawn and dusk conditions as well as to limit the lighting in my tank while still allowing me to see into the tank for about 10 hours a day.
For freshwater tanks, most fish do not depend so much on day and night conditions or need a light to simulate moon cycles, however some FW fish get 'scared' or become skittish by lights that just pop on and off all the time. For this reason, I use timers as well but only one of my two hood lights turn on in the morning, about half an hour before the other and then vice versa at night time. From my experience, FW tanks can really be affected negativly by long periods of light as this promotes algea blooms and allows cynobacteria to flourish.
Hope this helps at least a bit and by the way...Welcome to the Forum! It is good to meet you and I promise you, this is a GREAT place to gather info and get questions answered! | 
