Some observations --
I'm fairly new to chicken breeding, not an expert by any means. Please keep that in mind. :-)
Last week I pulled some eggs from my incubator for my good Silkie broody. Although all six had been in the incubator the same amount of time, two candled vigorous, two a bit behind them in development, and two candled inconclusively. (I stink at candling.)
The second day she kicked out the inconclusives. I was pretty sure they weren't good...