I would think you would leave it open so the heat would come out of the hole and condense above the inner cover instead of below. That way it may not drip back down on the bees. I also have an upper entrance that I am going to leave open. BUT, that is just my thinking, no experience here.
Moisture condensing is much more dangerous to the bees than heat loss.
Always leave a way for the evaporated water to be removed from the hive. Years ago, beeks would drill a 3/4 in. hole near the top of the top box. It was for keeping the hive dry and an upper entrance in deep snow.