Assuming we're talking about civil certified aircraft here, there's something that should be clarified in a previous post...
There is no such thing.
14 CFR 25.149 (to amdt 25-84 if we're being precise) has no requirements for reaction time in determining Vmc (=Vmca), nor Vmcg. In fact a 2 second reaction time for the latter test would be mightily exciting.
I believe the confusion is arising from the takeoff speeds requirements, 14 CFR 25.107(a)(2) to be precise, which requires that V1 be not less than Vef plus a time interval for pilot reaction, and also 14 CFR 25.107(a)(1) which requires that Vef be not less than Vmcg. Together these paragraphs require that V1 be not less than Vmcg plus a reaction time (2 seconds) BUT that is a reaction to begin aborting the takeoff, not a reaction to keep the aircraft on the runway. That is assumed to be a great deal faster than 2 seconds. (And is shown to be so during normal Vmcg tests)
The only variations which can be applied to the Vmc values are airspeed indication corrections (the technical analysis will be completed with fully corrected speeds, but information for crew will be "indicated" speeds).