First time I have raised chickens. I have 6 Buff Orpingtons and 5 Black Australorps. One BO started laying 6 days ago, I have gotten 4 eggs from her but she is the only one laying so far. They are all the exact same age & all raised together. They are 23 weeks old. Is it normal for one to start a week before any others? She is laying in the nest box in the coop, they free range most of the day, usually at least 8 hours & return to the coop at dusk.