As monopoly said, I used to do 12 on 12 off but with me working in the day and out the house. I turn them off at 9pm then get a family member to turn them on at 9am if not they go on at half 7am. But, anything around the 12on/12off basis is good
I go with sun up/sun down. I have my lights on a timer as close as sun up and sun down as I could get. The timer is a life saver! If you aren't home, the lights will turn on and off, plus it'll keep your cham on a schedule and they are relatively inexpensive at petsmart.