If you have the lighting on a timer I would suggest 8hrs. total time or only slightly more. Splitting the photo period several have claimed slows algae growth but I can't confirm that. I chose to do this and vary between 4/4 and 3/5 on my tanks. The times are in the morning for feeding young fish and on again when we are normally in the rooms to enjoy the tanks. You can always adjust things as you go but beyond 8hrs a day doesn't seem to help the plants much if at all.
hope this helps.
its pretty well written.