Mileage.

As long as you're more or less using your car regularly (at least once or twice a week) even if it's only for short distances, then using mileage as service indicator is fine. That what I've been doing all along for more than 20yrs of owning various cars. Most of my cars only run about 5-15k kms per year, never had problems following mileage even though workshops also suggested to follow duration (which I think is also partly their ploy to get more money out of customers).

Well warranty has time validity too. But if you're question is if still within the warranty period and your service is purely based on mileage, would it still be ok, then I believe it's still fine. Case in point is my current Livina which I bought new in Feb 2011 and so far has only reach 35k km, still ok to claim any defects (aircon coil, steering bushing, alarm repair).