I would have thought there would a replacement interval on the belt, obviously not as important as something like a cam belt as the engine will just stop if the belt gives up. I wouldn't have thought the loading on the belt would be as high as if it was running a cam and all the valves.
Very easy to visually inspect the belt by removing the cover, you could then start and stop the engine a few times to check it all. If the teeth on the belt have cracks at the root or the belt looks frayed anywhere then I would replace it.
Karl.