The general rule is to keep firing until you run out of ammo or the threat goes down, whichever happens first. One shot and run can get you killed, depending upon the exact circumstances. If your opponent is armed with a gun, you're probably going to hit from the side (as you turn) or behind. As for the one minute (or forty seconds) thing, well if he's got a knife and he closes with you, you're toast unless you're pretty lucky. And he might be a faster runner than you. Adrenalin (and God knows what else) sometimes gives people surprising abilities. That includes assailants.