Who is using them. How long do you find it takes to dry the car? Do you close the doors with it in there or do you leave them open? And anything else you can tell me about them. I want an extractor and I think a air mover might be a good investment as well.
Typically 90 minutes, or longer. A 'must have' in northern winters! I'd have condensation within 10 minutes of taking the car outside without the air mover. I leave a small opening for intake, and another for 'exhaust' of the humid air.
Typically (95% of the time) we leave the doors shut with the window cracked enough for the power cord. If it is real cold we put a towl in the window to "fill in" the hole and let the air mover run for approx 90 minutes.
Summer time we just leave the windows cracked on both sides of the vehicle.