I'm probably jumping the gun because it's only day four, but I have a pretty powerful egg candler and of my 16 coturnix eggs I can see clear vasculature in 3, darkening in 5 more, and then some eggs that are barely not glowing, but still not as far along. They're spread throughout the incubator so it's probably not a temperature thing, but I'm wondering how much variation there is in development in the first week. Can the eggs lagging behind catch up?