How short is too short?
My personal dryers have 14 inch rigid pipe straight through the outside wall.
I have 2 Maytag dryers,one on each side of a Maytag LAT washer.
Both are vented the same. Obviously never had a single clogged vent issue.
Drying time depends upon load size and type material.
All loads dry in 40 minutes or less.
Neither vent has a damper on the outside pipe.
If the dryer vent is of the type that goes straight through the wall (approx 12-14 inches) this can cause complaints of:
LAUNDRY NOT DRY AT END OF CYCLE
While this is not as common of an occurrence as vents too long--it is something to be aware of. Frigidaire & LG had discussions about this during training.
In a nutshell--the air flow from the room-to-the-dryer-to-the-outside-vent is too fast. The air drawn into the dryer from the laundry room is not able to be sufficiently heated (not enough back-pressure).
Adding a 90 degree turn to the exhaust vent (or rigid elbow) cures this problem.
I do not see this with every brand of dryer though.
Several times for Frigidaire. Once or twice with the LG.