I have eggs in my incubator right now that are on Day 5. Out of the 17, 9 of them have definite veining and heartbeats. The others I can hardly see the yolk and seem clear. Could these just be taking longer to form, or are they simply not fertile? It seems like the entire back row is not forming while the others are. Could they not be getting enough heat back there? If Im able to tell with the rest that they are a live, should I be able to tell with them all by now? How long should I let them stay in there, and how long can I wait to remove them before they explode in my bator?