Im a low mileage user, will do my timing belt at 7 years, which will be about 12,000 miles. VW GB dealers give all sorts of difrerent answers, and VW in Germany are now suggesting the timing belt is a lifetime fit. I'll go my own way on that for the peace of mind.
The oil pump belt is intended to last the life of the vehicle. In most cases vans work hard for a living and are dead inside 8-10 years, which the belt easily manages.
However, us leisure users make our vans last far, far longer than the average van buyer, and were starting to see the odd 5.1 with belt failure.
You can help things along by using the correct VW 507 spec oil, which was also designed to be kinder to the belt, and by replacing the belt at high mileages or advancing years.
But the belt is fairly chunky and manages a very light load indeed compared to a timjng belt, and problems other than in old age are thankfully very rare indeed. Its not really something to worry unduly over.