Actually they do continue to charge you until the car is checked in - unless you are lucky enough to strike a deal with the manager before your rental starts (I worked for a rental car company, so I'm sure of this) Seems like you might not be aware of how rental car companies operate as is referenced in another thread you started...Hope Hertz isn't the company you "forgot" to pay parking tickets from on this thread:
http://www.flyertalk.com/forum/renta...ntal-cars.html