I put a tiny roost into the bin with my week old chicks and they started using it on and off almost immediately. They're 2.5 weeks old now and will sleep in a chick raft on the floor, roosting on the roost and sometimes roosting on their feeder to sleep. I've not had adult chickens before, but I have seen a number of people posting that you may need to shoo the chickens into their coop at night for the first few weeks until they understand that's where they're supposed to go at night - that may be the issue more than the chickens not using the roost?