60 days to me is the norm Inc period. I leave mine completely Alone and let them pip. Sometimes us humans get in our own way. This year my first clutch of the year was incd at 88-89 they pipped on their own at 64 days out in 24-48 hours. Years before I've had them go to 65. But most hatch around 60. I hate cutting and I avoid at all costs. The only time i will is if everyone else has pipped and 1-2 haven't and days have gone by. Impatience is the only true reason to cut really before actually knowing there's an issue. If they haven't cut the egg and the eggs are candling fine, everyone is fine. Lower temps will lengthen your Inc time. Higher temps lower it.
I look at it this way. Even though I'm truly excited to see my little ones come out. I beleive that more issues can be caused by cutting too early. Look at all the work. Flushing etc. Bacteria growth etc. I prefer to let them do their most important event of their lives and thats pipping.
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