Lot said already about the cheating but hope you're billing him for this. If you showed up late for your accountant, dentist, doctor, psychologist, golf pro, personal trainer, Lawyer, etc. you'd get a bill.

I bill "contact time" (no distinction between ground/flight). But I don't stand around and drink coffee while you pre-flight either; I'm there every time asking questions, and getting paid for it. I understand emergencies, etc and I account for that but when it's a problem I start the clock. That usually solves the late problem.

Had to do this with a lawyer - when he squawked I turned it back on him, "would you bill hourly if YOUR client was 20 minutes late? Does that affect your professional income? Mine too." Problem went away.

See how dad feels when the $$$ is wasted. Would dad expect to get paid for his time?