Hmmm, I think I would wait till day 7 or even 10. It is very hard to see early development in darker eggs, so sometimes they need some extra time. Detatched aircells are a big problem when it comes to shipped eggs- its the post office, they toss the boxes sooo much. I always get a few with bad aircells. Sometimes the chicks still hatch though, so I always give them a chance.
If you decide to open any, you'll want to wait, and keep the egg out at least 12 hours at room temp before opening up the egg that was in the bator since the yolk will be all hot and runny and wont hold shape for you to look for the fertile bulls eye. You probably wont be able to see if the aircell was messed up though.
If you got your eggs from a BYC'er, I wouldnt worry about fetility- BYC'ers have a reputation to maintain, and are a pretty darn honest bunch. I've ordered eggs from a few of them and NEVER had any fertility issues. The only problems I've ever had are PO related only.
I wouldnt give up on your eggs just yet- sometimes its hard to tell at first when its early. Give 'em some more time.
Oh and check your temps, a low temp can make the eggs develop slower, or not at all (sorry if ya already knew that!
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