Basically speaking, if it's quiet- leave well alone. They 'should' last the life of the car, but many fail at low mileage.
You get plenty of warning though, a loud rattle means it want's doing.

I've just done it on a 65k car, relatively involved job and the locking tools are VERY usefull.

 

i'd change it now 52,000 on the clock, do your water pump too, they are common to fault and very easy to along with timing

p.s a chain should last near double a timing belt, belts are for say around 40-60,000 so your choice, but better safe than sorry sometimes eh!

 

Mate... changing a chain if it's not noisy... is pointless!!! (and very expensive)

 

as above if its quiet don't touch generlly timing chains don't need changing. they should last the life of the engine

 

Hi and thanks to all of you for the helpfull advice.
rnbrog.