VERY LONG TIME. the injectors are lapped in the 2-3 mic range from factory, and a 2mic absolute filter will ensure that no particles that pass though the injector are big enough to cause abrasion. Keep the sulphur content down and they live happy long lives. Factoid of the day... Sulphur while it used to make the diesel slippery changes is molecular shape under high pressure that is found in CR type set ups and becomes an abrasive molecule that will start to wear the injector.
Cat 1R0750 2mic filter is the best i have found so far for fuel that fits on the standard FASS set up.