In my experience, it is normal. They may still be bearding, if they were doing that earlier. But take a closer look--are some of the beating their wings very fast? They're cooling the hive. Many bees at night will beat their wings fast and direct air into the hive. Sometimes it looks like a relay, bees pushing air to other bees. And then finally, wouldn't you like to sit out on your front porch on a nice warm summer evening?.