lol that's sooooo true about work however they are first timers so it's possible they could quit early. It is odd that the know. I think it's more on the weather, once the weather is a certain temp/humidity then they go broody!! That's my guess I'm thinking there body temps are changing so they change with the weather. Because why would they go broody in the middle of June. Why not July, or March when it's decent. I have had a couple of mine go broody IN the snow. Omg she was buried in the snow last year but she was not giving up. Needless to say they didn't hatch but she tried. Lol. So I guess you have a very good question on how they can do it sooooo well and each time too. Hum now you got me wondering.
I've watched everything they do but never thought of the broody timing.