Need help with formula to calculate Pilot's Duty Time in 24hrs

Hi, everyone. I am a flight dispatcher who is having difficulty with a Flight Duty Period tracking sheet. I need a formula which gives me the total duty time of a pilot in one single day, which is calculated by using the DUTY START time of first flight and DUTY END time of last flight in the same day.

I have attached the excel file. Please download file and open the FDP tab from the file and goto cell AI7.

Basically I need a formula in cell AI7, which checks up the date on column D and selects a date range of the same date in column D (in this case D7:D8) and then give the difference between the Duty Time START of FIRST FLIGHT (column AF) and Duty Time END of the LAST FLIGHT (column AG).

Ex: 12:05-9:20 =2:45

Please note that I want the formula to automatically check the cells in column D for the dates, not manually select the dates, because pilots do more than one flight per day sometimes and it is never same. Formula than should be able to calculate the difference between the largest number in column AG and lowest number in column AF in the same date range mentioned before.

Uneven number of flights on different days is making it complicated for me, I am sure you guys would be able to help. Please reply at your earliest convenience.