Douglas & all,  Yes, this does seem a perplexing problem until you
realize that you do not actually fill the length of tubing -- only
enough air enters to reduce the pressure in the entire vessel (in this
case, the length of tubing) to move the pouch.  Granted, there is some
friction in the length of tubing that there is likely a minuscule
variation in time from the long tube to the short tube.

It might help to think of the tubing as a large air tank.  Say, for
example, the tank is under a slight vacuum.  If you have a valve at
one end of the tank and open it momentarily, the vacuum is reduced in
the entire tank, not in just the area near the valve.  A gauge
measuring the vacuum at the opposite end of the tank will instantly
(as much as the gauge mechanism allows) register the change.  Now
stretch that tank into a long tube, and you'll get the same effect.

Hmmm -- is this clear as mud?  I'm no engineer either, so I'll let
others chime in here!

David Dewey