Candle the eggs. If you've never candled it's as easy as grasping around a flashlight and to make a cone extension then set the egg on the hole in your hand. Shine in fat end of egg then tip to side. Do this at night, dark room. At this stage you'll only see a black mass but will easily see the size of air cell.
This diagram has 7 day cell size rather large but you'll want something at least that size and if up to 14 day size your definitely alright. The expected day of hatch is same day of week you set the eggs. If you did so on a Saturday you've still time to dry it out. Keep the water out until late day 19 or even day 20 if you don't see eggs rocking or hear a chirp. The larger you can get those cells the better.
The other thing to note is if your using a built into incubator hygrometer those are never close to accurate. If a small combo unit you tossed in incubator you can do a salt test on it to calibrate for accuracy. Basically I've seen them off quite a bit. Once calibrated you know the true RH.
Salt test:
Pour salt into milk/juice cap and add drops of water until saturated. I pour off standing water.
Put cap and hygrometer into a sealed container. I use quart size ziplock bag.
After six hours at least, or until stable reading, take the RH reading and subtract it from 75. The resulting number is your calibration. Always add that number to your readings for true RH.
Ex. your reading is 82% RH. 75-82= -7. You'd always subtract 7 from reading for real RH. Write the calibration number on masking tape and stick it to incubator lid as reminder.
