Marie, as long as they look good and you have new brood in your primary hive body below - I wouldn't worry about your schedule too much. If they are building at a good pace, then you can put that honey super on somewhere in July.
I would go into the hive right before you do this (or the day of) and look through both your bottom hive body and your top hive body and check to see that the queen is laying well and that everything is progressing as it should.

Thanks, beegeek
But I'd still like some thoughts about the bees clustering at the entrance. It has been raining for 3 weeks and I wonder if moisture is accumulating in the hive. Are the bees fanning? Should I open the top of the hive a crack to increase ventilaton? What keeps the rain from getting on the frames or is a half inch not important in that regard?

Thanks, beegeek
But I'd still like some thoughts about the bees clustering at the entrance. It has been raining for 3 weeks and I wonder if moisture is accumulating in the hive. Are the bees fanning? Should I open the top of the hive a crack to increase ventilaton? What keeps the rain from getting on the frames or is a half inch not important in that regard?

I find they do in a strong hive with lots of bees on warmer day's, if you have a top entrance or hole of some sort so the
hot air can escape you should be fine, sometimes on extreme hot day's you can prop up the top super one side with a small
shim.

Konrad

I propped the top open an inch and the bees no longer cluster at the opening. My bee=lady said with three weeks of rain the water content of the nectar is very high. She is getting other calls about this behavior, and realized the package is six weeks old. She wonders whether the now grown field bees haven't been able to get out to do their thing because of the constant rain. Interesting thought