I would define that as the time where you meet up with the bad guy in your house. How would you define those two things?
If "I meet up with" someone in the house, it will almost always be a matter of his coming to me.
Unless I am certain that someone in the house poses a clear danger, I will not be quite ready to shoot when I hear him or see him.. I will have to recognize danger; draw or otherwise access a weapon; and then, just maybe, shoot.
None of those things will happen instantaneously.
And I seriously doubt that if he does present a threat, he will be standing still.
I really don't see how that would differ all that much from what we see in Tueller exercises outdoors.
So, do we mean the distance from where I am to where he is when I detect the presence of a possibly unwelcome guest? To where I see him and decide that there is a threat? Or if I happen not to be carrying at the time, the distance from where I access a weapon and where the intruder is at
that time?
Or did the OP mean the actual shooting distance?
All of those would be very situation dependent, and in our house it would all depend upon where I am at the outset, where the person makes ingress, and what it is that alerts me to his presence.