An egg does not have 24 hours worth of development 2 seconds after it is placed in the incubator. It takes 24 hours for an egg to have 24 hours worth of development. 24 hours is considered a day. If you put them in at 9:00 a.m. on a Wednesday, they will have 24 hours worth of developent at 9:00 a.m. on Thursday morning. In theory eggs should hatch after 21 days of development, not 20 days and 2 seconds.
An easy way to figure theoretical hatch date is that the day of the week you set them is the day of the week they should hatch. If you set them on a Wednesday mornng, chicken eggs should hatch on a Wednesday morning three weeks later.
The fly in the ointment is that chicken eggs often do not hatch exactly 21 days of development after they are started. To start with, hatch is not an instantaneous process. The chick internally pips. Some time later it externally pips. Then some time later it zips and emerges. During this time, it is absorbing the yolk, drying up no longer needed blood vessels, learning to breathe air instead of breathing a liquid, and who knows what else to prepare to hatch. This process can easily take well over a 24 hour day.
There are also many different things that affect how close to 21 days of development it takes for a specific egg to hatch. Average incubating temperature is a big one. If the average incubating temperature is a bit high, the egg can hatch early, sometimes more than two days early. If the average incubating temoerature is low, it can really be late. Heredity, humidity, egg size, how it is stored before starting incubation, and some other things can also affect when it hatches. The 21 days of development is a target, not an absolute time.
Lockdown should be after 18 days of development. There are different things going on with lockdown, but a really important one is to have the humidity raised when the egg externally pips. That reduces the risk of shrink-wrapping the chick. With all the possible things that can cause actual pip to vary quite a bit, the absolutely exact timing of lockdown is not real critical as long as it is before the egg pips. I think it is good practice to go into lockdown after 18 days of development, but it is not absolutely necessary all the time. Being off several hours is not that big a deal as long as it is before pip.
? Just wondering because no matter how i do it i am always off by a day.
