Why not judge by hours? That's how most equipment is judged. I mean, heavy earth movers wouldn't do well on a 3000 mile oil change schedule. They might not hit 3000 miles for a year or more. It's just that anything that goes over the road is easily measured in mileage.

I had a yacht customer one time. He was the maritime equivalent of a spinner. This guy had more hourmeters sitting around his boat than the local marine store. They all ended at the same amount of hours. Finally I asked him if he still wanted them, because I could reset them and use them elsewhere.

They were all "broken". Probably the same as the "broken" odometer on his low mileage cream puff Lincoln. I'm wandering, though. What the heck. I think hours would be an interesting and accurate maintenance schedule.