timing chain on 2003 Nissan Altima

How many miles should be on the vehicle before replacing the timing chain

2 answers
The timing chain is not a regular maintenance item. It only needs to be replaced if there is something wrong with it, or if major engine work is already being done and it makes sense to replace the timing chain, too.

A timing belt, on the other hand, is a regular maintenance item, and the recommended interval for replacement is always published in the owner's manual.
This engine has two timing chain (an upper and lower chain), they are not a maintenance item but I have seen problems if the engine oil has not been frequently changed.