I agree that 8 hours is plenty. As to when you set it, it depends when you are in the house. I'm in all the time, but I spend most time looking at the fish in the afternoon/evening, so my light comes on at 2pm and goes off at 10pm. When I set up my new tank in my bedroom, the light will be on later - probably going off about 11pm. You can buy timers from the supermarket for a few pounds - they are well worth it!