A much more experienced beek told me that, I was asking the same as yu, about flights in an out. I was told that somewere over 80bees a min meant that the supers were filling up with either brood or honey, something to do with the amount of bees available to forage. I don't know why its that way but for example I have a hive now with 160+ bees going out, so approx 320 round trips per min, well that hive has the seventh super on it, and still a month and a half of goldenrod flow coming, Granted med supers but still. I guess it has something to do with room availabe ifthere full there is more bees available to run around, if there working inside they need more bees inside. and that hive was a new package.!!
I grant you it is strange but I have a hive a new split, it only has 6 frames full, I only see 40 bees one way, there aren't enough bees to cover the brood so they stay behind, just my thoughts but the brood area isn't full of brood yet, about 4 frames of brood.No super needed. I have another with barely 20 bees a min, its got also near 5 frames but only 2 are brood, no need to add, don't ask me why it works butyou can see the ratio of bees, but now the ones with 80 bees, have full boxes of bees and brood or honey, time to add a super.
I imagin its just some ratio of bees in hive to foragers, Just my thoughts. I am sure someone with more experience could add to this, either to say I'm wrong or right. Or explain the rational,
try it you'll see that i'm right, if you got 80+ one way flights check the top box. see how close it is to needing one. I'll bet its pretty close.