I'd gather that your measurement of time is a little off due to the adrenaline dump / battle-stress because 5-6 minutes of fighting in a streetfight/attack is a heck of a looooooooooonnnnnnnnnnnnnngggggggg time.
Anyway, we should not try to justify a reason to kill, because a judge and jury may feel otherwise. We just have to prepare for the worst, and hope for the best. Laws vary from state to state, but in NYC, you have a duty to escape. If your state of mind is to kill, you may be subject to a murder charge rather than a manslaughter charge (justified by self-defense).