The eggs in the incubator are on day 17, however the air cells seem small compared to the picture of the aircell on day 18 in the book (Gail Damerow's Guide to Raising Chickens)?? It says I should decrease humidity to increase air cell size? But they're due to hatch in 4 days and I'm not supposed to open the incubator after tomorrow?? So do I still need to increase the humidity for the hatch? What will happen if I just leave the humidity as it is? And NO I do not have a hydrometer.