Volvo used to put mileage and TIME in their manual for periodic maintenance.

Check your manual to see if the time frames are included.

If you look at an old timing belt, you might be surprised at the size of it considering how much work it has to do.

Also visit the Gates belt company site to see if they still send a free gauge to measure the grooves in the serpentine belt - new belts no longer crack like the older ones did. They wear out much like the tread on a tire does.

My dealer does not use those gauges, they think that you replace belts according their schedule - they might think that the belt is not so old.