https://www.backyardchickens.com/threads/day-0-on-a-full-22-capacity-nurture-right-360.1463696/#post-24396390
I'm doing this right now using two leghorn eggs for the pictures. Tonight will be day 4.
I literally only set those two eggs with the rest for the enjoyment and value of candling them. I didn't need those particular babies at all, because they'll only be a cross between a mutt rooster (brown egg layer) and a leghorn, but I am still excited to see what color chick I'll get and what...
I was able to see the heart beating on day 3 of a leghorn egg! It was so incredible. I tried and failed to capture it on video, but hope to try again tonight.