Our rule of thumb is after 12 pm doesn't count as the first day. Because we collect and store our hopefully fertile eggs in a cooler with a single ice pack changed out daily, plus tilting them back and forth periodically. Then when we have an incubator ready, they are about 60° F and take a few hours to bring up the temp.
Depending on the acclimation time we mark the start date.
To each their own. But this system yields best for our program.
The first day is 24 hours after you set the eggs. A simple rule of thumb is, if you set them on a Saturday, go to your calendar and count down three Saturdays. That will be your hatch date. Maybe. Even with broodies they can sometimes hatch a little earlier or later. Not as likely as with an incubator because your broody's temperature and humidity are preset to be ideal conditions for hatching. The 21 days is an average, not a hard and fast rule. That being said, if it's over 24 days, the eggs most likely aren't going to hatch.
Interesting, bobbi-j. We don't use broody hens anymore. If fact it's been a long time. So we learned something today.
When we did, they were hatching different days, sometimes a week straight. Chicks weren't in a safe atmosphere in our particular setup.
When we decided to start selling chicks/chickens, we switched to incubation for birth control and higher yields. Also our broody hens stopped laying, giving us less to hatch.
We never got technical on the natural process. Thanks for that info. ☺
Just hours after my post on this thread, today is day twenty in incubator #1. Last night or early morning not 1 but 2 chicks hatched and were completely dry at 6:30 am this morning. The were raising cane and soccer balling all my other eggs. So that is the earliest hatch we have ever had. Today is still day twenty and several others are peeps and jackhammering away. I resoaked my rolled up hot tap water washcloths and crossing fingers.
See something new all the time. Happy Sunday everyone..