Here is a topic of which I have only passing knowledge. My understanding is that it is the time from which the sear is released until the firing pin completes its forward travel, and it is measured in microseconds. If this definition is incorrect, please let me know.
More importantly, what is the effect of lock time on ability to hit a target? I would reason that a more precise firing mechanism with a shorter lock time COULD reduce movement of the firearm prior to the bullet exiting the bore, but I can see where that may not always be the case.
As an example, I just purchased a Spanish M1916 carbine (I have not yet fired it, but I'm not expecting great accuracy here...). The cocking indicator at the rear of the bolt travels about 2 inches (okay, so that's an exaggeration, but it is an unusually long distance compared to other bolt actions that I own). I can bet there is a lot of slop within that movement that would at least have SOME effect on the stability of the firearm during the firing sequence. I could conceive some sort of relationship between lock time and the amount of movement during the sequence. If so, is this "slop" measurable? If so, how? And for that matter, what device is employed to measure lock time?
I know this is a question for the 100 lb. brains on the forum and will get lots more views than replies... but I will bet that there are a lot of us who do not understand this very well.