My father used to make me 'earn' my TV watching time. It was one bucket of weeds for one TV show per day. So my sister and I were out there weeding away! I used to hate it but now I am thinking, that is not a bad idea!
For a more detailed guideline, see www.caringforkids.cps.ca/growinglearning/GoodTelevision.htm
Remember, you do not want the TV to be parenting your child and teaching them values and beliefs which may be contradictory to how you want them to grow up. The more prolonged the TV viewing, the more the impact of negative effects it will have on your child. You don’t want the TV to become their ‘real world.’