Unlike cars with timing "belts" a timing chain does not have a finite
service interval, but as said, it and the chain tensioner/rails, should be
checked. Usually, the tensioner starts to fail long before the chain
stretches out of spec. A good test is to listen to the engine on start up.
If you hear a chain rattle at startup that disappears when the oil pressure
builds up a few seconds later, that's a classic sign that the tensioner
should be serviced.