I just culled 10 of my 58 today - on day 8.
The dark shadow is the chick! so you are in luck.
I have not seen veins in any of my eggs - & no air cell - or at least one that moves around quite a bit.
So - my advice would be to leave them all alone for 5 more days at least. I culled 3 today that were good because I didn't see the 'spot' or shadow in the egg, but it was in there hiding.