Quickturn is a setting that can be set to define the length of a turnaround time being considered as quick turn.
In the settings menu you can fill in 3 values. The first one as the definition in hours of how long an aircraft can stand on the apron between flights and being a quick turn. The second and third value define the time window in which the flights need to occur for still being a quickturn. For example:
10 9 22
The 10 represents that an aircraft needs to depart 10 hours after arrival to be considered as a quickturn. The 9 and 22 represent the opening hours of the FBO. The 10 hours turnaround time need to be in this time window in order to be considered a quick turn. In case an aircraft lands at 21:00 and departs within 10 hours, it is still not considered as a quick turn because the aircraft needs to depart before 22:00.