Something I noticed when Canning (processing my food.)

I have noticed that when I add 5 more minutes to my Processing time, the weight usually jiggles within those extra 5 minutes and my processing time is usually right on time. Has anyone ever tried this or found this to be true?
Ex: Ground meat, 10# pressure, 75 mins pints, 90 mins quarts. I will set my pints on 80 minutes and sure enough the weight begins to jiggle within the first 5 minutes and leaves 75 mins processing time! Nearly every time.