In the UK most light aircraft are maintained on the Light Aircraft Maintenance Programme (LAMP). It specifies that maintenance is calculated on the basis of flying hours. Every commercial aircraft I have worked on over 40 years used flying time.
Block time or chock to chock as another variation has been used for charging customers for the time they have the aircraft.
Always thought it a bit of a rip of myself but there are arguments both ways.
I would say it does make a difference.
If every flight has a 10 min pre flight checks, taxi and warm up plus a 5 minute taxi and shut down that is an extra 15 minutes non flying time per flight (based on a one hour training flight). If your engine for example has a 2000 TBO you are loosing 500 hrs!!!!!!!
All your maintenance will be done 25% early and your bills will roll in more frequently. Nice little earner for the maintenance organisation. More downtime, more component changes and more maintenance interventions during the life of the aircraft.
Get another CAMO those guys are going to cost you a lot of money. Ask them where it specifies you have to use block time. I have never come across an operator or for that matter a private owner who used block time.