[MB75]

I keep the lights on for about 12 hours during darker times of year, and 8-10 hours summertime when there is lots of daylight through the windows anyway.
If there is an algae problem I keep 3 hours break with lights off in the middle of the day.

I would not cover the aquarium for the night. The reason for this is that at night the plants do not use carbondioxide and do not produce oxygen. Therefore the only oxygen is dissolved into water at water surface only so making sure there is good access of air to water surface is important.