I candle every single egg, tossing all of the clears and those that quit developing. I do this by day 10. I am not religious about exactly when. Somewhere between 7-10. No later than ten. The length of time that they are outside of the incubator is not critical, if not excessive. A mother hen leaves her nest to drink, eat, and defecate. You will do no harm. I have lost power, and accidently left my incubator off over night (twice). Each time I still had a reasonable hatch considering. If you are uncertain about an egg or two, hold on to them. Initially, you will be concerned about tossing good eggs, but after a batch or two, you will gain confidence in what you are seeing. You will do no harm to re-check them after a few days. Crack open the eggs that you decide are no good. Doing that, you will begin to be able to determine why you lost them. If they are fertile. It does help (it did me) to actually see it. It is rare for one to rot and explode. If you ever have it happen, you will never allow it again. It can ruin a batch. There are many charts and pictures online that illustrate the process, and trouble shoot problems. Mississippi State University used to have a very good chart for trouble shooting hatching failures. It was good enough that I printed it to keep as a resource. I am not certain whether or not it is still there. Ron, west coast Ron, would be able to point you to a wealth of resources concerning incubation and hatching.