I have a buff orpington who has decided to go broody. Yesterday was the first day I've noticed that she has stayed in the nest box all day. She only had one egg. I marked and added 3 more. If she's going to spend 3 weeks sitting, I'd prefer she sit on a few more. The one egg she had was up in front of her, peeking out from under her breast feathers. Will she lay more before she starts to incubate them or is her first full day of sitting considered day 1 of the 21 days? Would it be safe to add a few more today? How many could I expect her to realistically hatch? She is pretty young, maybe 8 or 9 months old at the most. Thanks for any input!