I've seen this asked a few times on Meta.SE and I believe this answer is still current:
How was this answer posted after this question was closed?
The message that you see not allowing an answer to be posted happens on the client side of things, the server allows a grace period of around four hours. So one likely cause is that Jim had it open in his browser for some time and that check failed. Or maybe he did the same using the mobile version of the site that according to that answer doesn't have that check.