Day 4 is probably earlier than I would assume anything definite about development. Some seem to show prominent veining early and some don't. I usually try to wait until day 10 or 14 to pitch eggs. The air cell is just developing and will increase in size as the embryo develops. You can pencil a circle around it to monitor the size of it if you want to. If the eggs are shipped I would probably minimize handling because their air cells have been jostled in transit. I don't know if there's a set expectation on shipped eggs...I have had terrible (10%) and have had 90%. You need to assess hatch rate based on what you received, what was unbroken, what was fertile out of what you received, and what actually hatches. For instance, last shipment, I purchased 10, received 12. 1 was cracked, 1 was infertile & culled day 10, and tonight I culled one blood ring on day 14. So, out of 10 viable received, we'll see what hatches. Be patient and handle them with extreme care & sanitized hands! Good luck!