AmericanMom - thanks! The egg could be as far along as 14 days - would you still toss it?
Anyways, I went out this morning when the broody was out having a quick dust bath and added some new hay to her nest. While I was out there I did a quick sniff test again and didn't notice the boiled egg smell anymore - weird. I'll check it again in a few days... After that point (when the oldest one is 17 days), should I just leave them be? I'm really annoyed at myself for not either marking the first couple eggs or moving Maisy/broody out by herself as soon as she started sitting on eggs. Now I'm dealing with a staggered hatch....next time I'll know better!
If your not smelling it then no, don't toss, a rotten egg will be a rotten egg period, Perhaps what you smelled was something else, it wouldn't come and go...