You are actually fairly safe just shooting them until you start to encounter a problem as the problems will usually start out at a very infrequent rate and provide a warning. Because they go gradually, you can still use the gun to finish up a shoot, etc. It will usually not start out at anywhere near the two "failure to fire" per subevent that is given.
Because they use coil springs that almost never really break but just get weak, typically you will get a misfire rate of say 1 per hundred and then slowly work up to the rate of 2 per 100 shots, etc. Once you notice that something is going on, you can remove the pin and make sure the hole it rides in is clear and then check the front of the pin for wear and/or change the hammer spring, etc.
Guns like many of the Perazzi and SKB's that use flat "V" springs actually break the spring itself and something then must be changed in order to fire the gun. It is really hard to say how long an individual spring or firing pin will last. I know of examples that broke quickly and others that lasted many years and 10's of thousands of shells. If you wanted to be on the safe side, then change the firing pin and hammer spring every two years on a gun that is being shot regularly.