I run my lights at night too. I started to move the light period by 30 minute increments as the cold started to settle in. Now my lights shut off at 11am and kick back on at 5pm. The heat during the day is enough to keep the plants warm so the light isn't needed to keep them warm. During the night the temps drop into the 50's so it's nice to have my light warm them up to about 75. If anything I think the ideal time to grow in my room is during the winter. I imagine the summer will be much more difficult to control temps.