Thank you ! I was worried that my current batch would end up bad but they seem fine. I think I was careful enough with the eggs, though I did have to travel through a flight of stairs. I might've put them in too early without allowing them to come to room temperature. Least I'll know for my next...
For some context, our bantam was broody last month and now has 3 lively chicks. She had a clutch of around 11 because of inconsistent checking and due to other chickens sitting on her to lay their eggs. (There are other nest boxes !) 4 were closer to lockdown and the other 4 less than 7 days old...