Night before last, I noticed a bantam missing at bed time. Hunted round, and there she was, under the bushes, sitting on 10 eggs. Not all hers, some are a different colour, so two banties laying there. Have removed her and the eggs and shared them between her and one other broody bantie, If left to their own devices, the hens would probably lay a dozen then sit. So the sitting does not start until all are laid, and 21 days from then.