My chicken babies are just over three weeks old. They are already basically fully feathered and can even fly vertically up to three feet. This is the ten day weather forecast for the area . The reason I ask is because most people who have been answered live in the southern states. I haven't really seen an answer for a northerner at all. If it is too cold, could I provide them temporary heat in the form of a heat lamp, and if so, for how long should I run it, on a timer for just the night hours?