Dynamic assignment means that the CALs are given on a frist come first served basis, instead of manually add any granted user on the list. But once the license has been assigned, you have to remove it manually. The complete removal of the assingment and so the again available CAL will be done after 24 hours of the license last use.
Apart from that, if you are using QVS v9, I'd suggest you to upgrade to the SR6 or SR7, because some issues with CALs had been solved.
Hope that helps.