I just found a stash of frozen eggs that a single girl had hidden (they were all the same size and shade of green). Little rascal! They're just going in the compost heap here since I don't know how old they are.
I had two last week when our temps were down in the teens. I checked when I closed the pop door at about 7pm but evidently somebody (probably the same hen) laid after that two nights in a row. I found each egg the following morning hard as a rock with a cracked shell.