The point about allotments is a good one, these are in a similar situation and I just moved the queen onto 14x12 frames so I'd rather chance two queen cells and the possibility of losing a cast swarm than have a lone cell fail and a grumpy hive or two on site. Ultimately because of the weather I didn't get much say in whether I left open cells or not. I left an open and a sealed cell in the Nuc as I figured that gave me time to assess the situation in the nuc and possibly remove that queen cell if all looked well otherwise, all the rest were already sealed. I guess I could have torn the lot down and left them for another couple of days but I felt under the circumstances that this was the best course of action.