If one were to do that, the results would be variable based on where in the country they are located. A chicken brooding in Florida will have different readings than a chicken brooding in Arizona or the Colorado Rockies. Add to that, the amount of time each hen stays off the nest varies as well. I have hens who run around clucking like crazy, eating and drinking as fast as they can so they can get back to their nest, while others take a more lackadaisical approach and stop for a dust bath on the way back to the nest. The latter's eggs will have longer to cool than the former's, yet in both cases they will hatch on or about their due date. Likewise, time of year will make a difference. My broodies are most active in spring and early summer but I typically have broody hens non-stop from about March to as late as December. The hens brooding in winter will experience a greater temperature fluctuation and different humidity than those brooding in the warmer months.
For that reason, I take a more lacadaisical approach to my own incubating than some. Rather than be a stickler about temp and humidity, I take a leaf out of the hen's book and realize that their conditions vary widely yet their chicks always hatch, so if I open the incubator and let the temp drop a few degrees here and there while candling, its not going to kill them. Recently I stopped increasing the humidity for hatch and now hatch at the same humidity they are at the whole time they are incubating. Guess what? Not a single sticky or shrink wrapped chick out of three hatches doing it this way!