That 1/2 second MATTERS.
There are reasons we have the Four Rules for Firearm Safety.
It seems to me that in situations like that where your life is being threatened, your insticts kick in, your adrenalin kicks in, and your only goal is survival. You're best chance as survival is to eliminate the potential threat.
Don't hesitate, and risk killing your wife who just got up to use the john, and risk jail time for it.
That's a different scenario. His life had already been threatened by these thugs and he had already identified them as being robbers.