Looks like Ester has taken over and Sissy is no longer broody. Ester went back to the eggs last night and was there this morning. I guess the heat of the day did affect her "schedule". It's been about a week now since these eggs were laid so I think we have a couple more to go before potential hatching?
It's actually relative to when they started being sat on full time verses when they were laid. I would probably try to candle at about this time to see if there is any development. With it being your first time though, I might not discard them if I couldn't see the development. But it is an amazing sight to behold the eye forming and the heart beating. But I guess having young ones, you've probably recently experienced that!!