Three different hatch dates, same incubator

[chickens really]

Definitely lockdown the the first two sets. Then once hatched drop humidity to accommodate the the later hatch till air cells are correct.

 

[FortCluck]

Keep in mind that humidity isn't a set number. In nature it varies dramatically from time to time. A couple days of high humidity won't hurt the younger embryos as long as egg weight loss is adequate.

I agree to this... My last hatch I screwed up and I had very high humidity throughout so my air cells were awful. I ended up losing nine chicks.

This current hatch that I am on my humidity has been on the lower side because I ran my incubator dry to see which method worked best in my location. The air cells are on point. I only increased my humidity to 48% for lockdown this time. Everything is going way smoother.

There is no definitive number, you have to figure out what works for your location and for your incubator. What works for someone may not work for someone else...