Most fan assisted incubators have a default temperature setting of 99.7 Fahrenheit measured at the top of the egg. I have tried various temperatures over the last few years, and using accurate thermometers situated at the top of the egg, I find that 99.7 degrees Fahrenheit (37.6 degrees centigrade) is the best temperatue to use. I run my incubators at 60% humidity throughout incubation.
After 26 days the keets begin to hatch. They need to be carefully watched at this point as old broken egg shells need removing from the incubator, otherwise they can get wrapped around a whole egg and give it a double layer, preventing hatching. Guinea Fowl eggs are 4 times harder than hen eggs which means that only fit, healthy keets will hatch. Sometimes keets need a little help after chipping, under the shell is a membrane which quickly dries out and traps the keet inside, I gently prise bits of shell off with my fingernail until the keet can get out of the shell.