I have to disagree with you there. There is absolutely no increase in the rate at which they call boarding groups before they shut down the VQ. If there was you would see the graph jumping faster than any other time of the day, but you don't. They might give them 2 hours to come back, but they aren't calling "1-2 hours worth of BGs."
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Hmmm... I was going mainly by reports of people finding the queue full with over an hour wait at the end of the day.
We could always take the first derivative of the curves to track the rate of change of calling BG#s.
Cool graph, is there a site the produces that?