I was just wondering when others do this. I pull eggs that have shown no "change" after about a week. If I have trouble seeing into the egg then I give it a few more days. I do my "final" cull of incubator eggs at 2 weeks - just a few days before turning stops. Generally speaking I have been able to see clear veining in nearly all eggs by 3-5 days. I use a mag light that is very very bright. Shortly after that the egg starts "filling up" and goes pretty dark by around 10-12 days along.