Just a thought, I have halides coming tonight, I know they make the tank hotter, if I ran them at night or evening rather than during the day is that a better idea?
I think it's mostly the heat generated by the ballists more than anything. Running them when the ambient temperature of the room is lowest would be best. But honestly I would run them when you want to view your tank. Obviously bearing in mind running long enough for coral to get light ect ect. In summer people run fans ect over water to keep heat down. But it;s hard to figure until you got tank up and running.