Charter companies normally bill flight time plus 1/10 an hour (6 minutes) per flight leg
With a minimum of 2.2 hours per day lets say you flew NY to FL on Friday night and back to NY from FL on Monday
Even though the plane may have only flew for 3 hours down and 3 hours of back ayou would be charged for 9.6 and hours 2.2 hours per day over 4 days