Timing Belt replacement on Duetto

1996 Duetto, 66k miles on clock.

Timing belt was replaced in June 2012, when the van had done 50k miles.

Garage who recently serviced it suggest timing belt change every five years or 50k miles, but our van has only done 15k since the last change.

Which is more important - the 50k mileage interval or the five year time interval? What is a timing belt made of? Is it likely to deteriorate over time if not used as regularly as a Transit is designed for?

Or should I just get it done?

Different van I know, but I replaced the belt on my Boxer when it was ten years old, in line with Peugeot recommendation, even though it had only covered 40,000 miles from new.
These commercial vans are designed to go round the clock umpteen times which won't happen with my van, so I'm inclined to replace the timing belt on a time basis rather than mileage. If I still have the van I'll be looking to replace the present belt when it's 7 or 8 years old.
Al.

It don't matter how many miles it as done, thats why it is 50k or 5 years which ever it reaches first. Not worth chances a cam belt cheaper than a new engine.

I tead somewhere recently that because campervans and motorhoms can sit for many months per year without the engine being turned, cambelts can suffer the same fate as tyres, which are known to "flat'spot" ie the sidewalls crack at 5he bottom from sitting months in the same position. The writer suggested halfing the recommended time between canges.

In the 10 years that I owned my Mk5 Transit I had the timing belt changed just once - when the van was 10 years old (sold when it was 15 years old).

I never had any issues at all, but I accept what pilchard says above - mine was used on a weekly basis throughout the year. If the van had been laid up for months at a time I might have been concerned enough to have it changed more often.