Number of Labor Hours for a Towed vehicle install?

I believe every one of those manufacturers list the number of hours it takes to install / accomplish those actions. My mobile tech told me the Air Force one was listed as taking 2 hours to install so that’s what he charged even though it took him 7 hours. Said it wasn’t right to charge for his “ going to school “ time for the first one.. Don’t know about all together, but seems high too me.