ISO 13406-2, A Much More Up-to-date Standard
Apart from the matter of dead pixels, the ISO 13406-2 standard defines flat screen response times as the addition of the full on and the full-off time. If you refer to the text published by the international body, it is the addition of the time needed to display a white dot from black, and vice versa, from black to white. Under this standard, it is not actually the total time that is measured but the time that passes between 10% and 90% of the required brightness. This also corresponds to the definition of "full-on time" in electronics. The problem is that in electronics, the measurement is not considered to be very reliable: It is merely an indication, because it is too dependent upon oscillations at the extremes.
Apart from the fact that the system needs to stabilize, you also have to take into the account the fact that a full-on time or full-off time taken between 10% and 90% could measure 20 ms, while it would measure 40 ms if the time between 0 and 100% brightness were measured. Yet this corresponds to the amount of time that would be needed to actually display the colors requested, and not an approximation of them, which is all that is required by the ISO standard.
In such a case, which screen would react the fastest, the former at 20 ms at 10/90% and 40 ms at 0/100% or the latter, given as 23 ms using the ISO 13406-2, interval but only 30 ms between 0% and 100% ?
To conceal this defect, the electronics engineers prefer to abandon "full-on time (FT)" in favor of "response time (RT)". A minor point, their RT is not the same as that defined by the ISO. In the former case, they are measuring the time taken to get from 0 to a stabilized state of the system. So theoretically, the response time is the time needed for the transitory state to disappear totally. In practice, the technical people agree that, based on the level of accuracy required, it is the time at the end of which the system response enters a corridor of more or less 5% of the final value without emerging from it. As far as we are concerned, this is once again a measurement of the time needed to get from 0 to 95% or 105%, without any signal being produced during this interval.
If the time measurement adopted becomes that created by the electronics engineers, that would be better, but it's still not good enough.