Not a lot, make sure they have food and water, and that they are sheltered from predators at night. We have six hens and a rooster. The work consists of cleaning the coop once a week, and at the same time clean and refill the water dispenser and fill up the food reservoir. My kids do this in half an hour. We also have to pick up the eggs daily. We raised our Brahma chickens ourselves after hatching them in an incubator, and they are wonderful pets.

Edit: because we feed them a more varied diet, the eggs also taste better.