And here's what wiki how says:
As soon as possible you need to immobilize the chicken and splint the leg. position the leg straight, and pad the splint so it will not rub. popsicle sticks are a convenient item to make a splint out of. make sure the splint will not poke or irritate anywhere, and keep the chicken in a small cage or even a box for at least a week. During this time make sure he has plenty of food and clean water available. Since chickens cant see in the dark, if he was in a box you'd have to take him out a couple times a day to feed and water him. Check the splint often, and change it if anything seems wrong. keep an eye out for infection if the skin is broken- antibiotics may be needed. Chickens can heal amazingly fast. I would keep a splint on for at least 2 weeks, I dont know how long it takes for chicken bones to heal. Human ones take 6 weeks.