Corn snakes are primarily nocturnal, meaning they are MOST, active at night, but are often active in early evening as well.
I could be wrong ( hopefully someone will correct me if I am ) but with night time being their natural active time, it would suggest they prefer to be out when it is dark.
To run the light at night would seem to be counter productive in that case. Some folks use night time bulbs in their viv's for night time viewing, and that would still provide you viewing pleasure, without harsh lighting and would give you the ability to sleep with the light on.
Most folks suggest 8-12 hours of light a day for corns. Pick Up Bill & Cathy Love's Corn Snake Manual, it has all the info you could ever want, is superbly written. :wavey: