Well, whethere you turn the lights on at night or during the day is an issue best resolved by answering this question: When are you home to see your fish? I have my lights on from about 4 pm to about 4 am (on a timer) as I am usualy home by 11 pm the latest, but my girlfriend and the cats like to see the fish too. What's important for the fish is that there is a schedule for the light. You should turn it on and off at about the same time every day. And in roughly equal measure (hence my 12 hour on/off period). When you are around to enjoy your fish is when you should primarily have your lights on. It serves little purpose to have the fish if you can't see them.
\Dan