My Bourbon Red is up to 23 eggs in her nest and counting. I'm not so sure the nest box can hold too many more, it's pretty crowded in there. I have read the average is 15 eggs but what is the most you have seen?
I think it totally depends on the size of the hen! If i were you I would reduce it a little! Ive seen hens with 18+ and ok! How to tell if you have too many is to check the temparature of the outside egg- if it is cold she has too many under her and they are spending too much time on the outside (as she rotates them from the centre to the outside side!) If this happens you could find a few embryos die because they get too cold so it may be better to have too little than too many!
She laid another egg today but for the first time she returned to the nest after her evening walk. For about a week now she had been setting on them for about 6 hours a day, sometimes laying an egg and sometimes not. She would then leave them mid afternoon and return to them until mid morning. Today she went back to setting before the sunset. Hopefully this is it.