depends what kind of engine you have. Racing engines see a lot more abuse than engines such as the N12 for example. They have more power, see much more RPM and so just the tiniest flaw could destroy it in a matter of seconds.

It doesn't mean that every rod has a "used-by" date, some can last 10 litres without needing to be changed, some can only take up to 4 litres of use.
It depends on how the engine is maintained and how it's designed really.
Just replace it when you think it should be replaced or you have doubts about its integrity.