So on for 1 microsecond and off for 999 microseconds @ the factory rated CW current shouldn't hurt it at all or reduce the MTTF unless you have a noisy signal, but a square wave at the factory rating won't wear it out like a tungsten light bulb element, now there's something about a ramp up being a good idea when over-driving but pulsing is what they do sending data all day long, do you not have a data sheet ?