- a call can span several hours or occur inside of one hour
- summing the difference between timestamps in a group by query gives
a sum on time that BEGAN in a particular hour but doesn't figure in
that after 3600 seconds, you are in a different hour!

I typed this all out and accidentally pasted over much of the
explanation I hard originally enterred. My tip for any other posted,
author your post in Word where you can UNDO!

Thanks to all of you for reading, and for any advice you can leave me.