I have a chart that shows development for all 21 days. Anyone that is interested can email me and I will email the photo. They are actual eggs opened at each day of development. Pretty graphic so I don't want to post them but I will be happy to share.
Is the entire inside dark, or is it just that they are dark eggs and you can't see. If on day 8 and they are completely dark, I would pitch them. Check out this website.
http://www.shilala.com/candling.html