Depends on who you ask and you'll get a lot of answers. Here's our method.
In cool weather (less than 80 degrees) we feed and keep them lighted 23/7 with few if any problems. Feeding them 20% feed, constant water, and 23 hours of light can result in close to 8 pound birds in 8 weeks.
When it gets warmer we usually turn of the light and let them eat a little less and rest a little more. We also let them on grass .