So the temp is low.No, all my thermometers are calibrated. I always incubate at 98.5°F - 99.5°F.
I've had chicks hatch under a broody hen on day 24.
Silkies, I incubate at around 97.5°F - 98.5°F. They seem to do better incubated at a cooler temperature, & usually will hatch on day 21, & 22.
To each his own. All chickens' eggs need to be at 99.5.