Would this require a 9 hr rest period.--- Starting when I drive my car away from the airport.
If all you are doing is that scheduled run, and your Operation Specifications specify that 135.265 is applicable then yes - there is no use to remaining on duty. However, if you want to juggle the flight instructing as well (with the same operator), therefore you could at the beginning of the week (after 24 consecutive hours rest):
1 The latest you could go on duty at 21:30, fly 5 hours, remain on duty to instruct another 3 hours until 12:30, then leave, take nine hours rest (away from the airport), and go back on duty the following duty day at 21:30 again.
Or (Assuming you finish your freight flying at around 4am)
2 The earliest you could go on duty - 1300 fly up to 3 hours with students, then fly your frieght as usual and go off duty at 4am (as scheduled/expected).
It would be dictated by the first duty day of the week, after the 24 hours consecutive rest in 7 consecutive days.
On your flight manifest there should be somewhere to write the time you go on duty, amount of rest you got prior to going on duty, time off duty, and time available to go on duty again.
I'll go out on a limb here, and say that you go 'on duty' when you arrive at the airport with the intent to fly - the drive there doesn't count - and off-duty when you leave the airport after you're done with your paperwork.
Your Director of Operations is really the one to ask. He'll be totally familiar with your Operations Specifications (has his signature all over it), and has operational control over you, as a line pilot. Assuming s/he wants to keep their job, and violations to a minimum.