Question on incubation of chicken eggs

[SilverBirds]

At the moment I am incubating some eggs just to see if they are fertile. So I don't want to hatch them. It sounds like that at about day 3 and on I should be able to crack the eggs open and see veins if the eggs were fertile. Right?
Thanks

If you crack them they will definitely have veins if they are fertile. I had a hen go broody had to break her. My brother cracked one of the eggs open and the yolk had tiny veins running all through it. The egg was 2 days old.