Ttopendtorque:
We could debate the 1 vs 2 second rule for a long time. There is evidence (and experience) that 1 second isn't long enough - it's hardly time for the 'this can't be happening to me' to flit through your mind. 2 seconds with no reaction on any controls is too long and unrealistic on the other hand.
From my experience, if you use the same criteria as was used to develop the HV curve (no matter which intervention time), the HV curve is a valid indication of the area to avoid. Sadly, a lot of hot-shot instructors think they can demonstrate that they can 'beat' the HV curve - but they do this without understanding what the curve actually represents.