overtime for a tanker

Hi,

i have to create a report for overtime......Find below my scenario

Report : overtime for a tank-- loaded /unloaded ....

9.00 to 18.00 is the working hours....we have to calculate the overtime from present day 18 hrs to next day 9 hrs.

logic involved:

1.Tanker come inside between present day between 9 to 18 hrs & leave between today 18 hrs to next day 9 hrs

2.Tanker come inside between present day 18hrs to next day 9 hrs & leave next day between 9 hrs to 18 hrs hrs

3.Tanker come inside between present day 18hrs to next day 9 hrs &leave next day 18hrs hrs to 9 hrs

4.Tanker come inside between 9hrs to 6 hrs & leave next day 9 to 6 hrs

I have to calculate based on Entry slip create date & time with gate pass create date & time for a vehicle.

when i run the report for a calendar day it should display the the overtime fro the particular tank.

Kindly help me.

Regards

Karthika