I think incubation formally started Monday. I had thought that it started Friday or Saturday, but there wasn't a lot of down and nine eggs at the time. Non Birding Bill and I stopped at the store last night and I took a photo in the box, there's LOTS of down which is a sign of serious incubation and now there are 11 eggs!
Note the gray downy feathers to keep eggs nice and toasty. I wonder if it's uncomfortable for hens to incubate on hot, humid days while crammed in a box? The anthropomorphic side of me makes me wonder if hens complain to their offspring, "I sat in a dark box in 100 degree weather for four weeks for you!" Much the same way my mother likes to remind me I was three and a half weeks late during July weather when she was pregnant with me.