It can be simplified further ...
Maintenance time is the time between the wheels leaving the ground and the wheels touching the ground. How this is recorded is up to the operator but could be taco, air switch or watch time.
What you pay for the aircraft is also an operator decision but is usually startup to shutdown time. Again, how this is recorded is up to the operator but a “Hobbs” (brand) meter is common, it starts when the oil pressure activates it and stops when the oil pressure stops.
The difference between the two is around 0.2 per sector or lesson. This “guestimate” is 6 minutes till airborne and 6 minites after landing till engine off. Pilots log time in command which is usually considered as startup till shutdown.