Might be a bit aggressive....
I did my belt yearly...but my tensioner was 10 years old...had the factory one and 100,000 miles when I sold it...maybe I was lucky...but just monitored it...was fine. Things are good till they fail.....strut was fine and spring good, bearings fine...so I kept mine original OEM...
Sure...I did not track my car, but IMO you should get 40,000+ miles from a tensioner minimum....
I've been through a whole pile of tensioners. I've had them fail in as little as a year. Usually it' the bushings that fail, then the thing pretty much rattles itself to death.
well, the one I took off was original, 90k miles, and the belt slipped when just looking at the throttle (belt had been replaced 3 times).
My logic on all this is: a lot of stuff on this car breaks at an alarming rate, so fix it before it spoils your appetite to keep driving this thing. I come from 20+ years of Toyota ownership, so my reliability meter has a slightly different scale to it than what others may consider normal. But I love the car, so I keep throwing parts at it to keep it as close to reliable as feasible.
Thing is, all these maintenance parts I regularly swap out before they fail amount to less cost than a single monthly payment on a 2015 Mini.
Check also: Alternator. They have an annoying habit of going bad at 70-90kmiles. Daughter's alt actually cracked the case nearly in half when it failed - sounded like a supercharger rattle but was the alt. And if you're getting at the s/c, be sure to change out the alt brushes as well, $11 part...
