I haven't tried my hand at chickens yet but if they work the same as every thing else they will eat once every 10 real time minutes with the first one for that day being right after sun rise they have a 33% chance to reproduce once per day (checked every 30 seconds after being fed) if a player is within 64 meters and there is room in the enclosure. Animals will not path to food that is farther than 10 meters away from them so if you have an extra large barn you may have to drop food on both ends.

If no player is within 64 meters when they eat they will not reproduce. Its best to drop just enough food to feed each animal so that you don't waste any resources.