It's weird that self-defense has this time limit on it's validity. Like if someone tries to kill you and you kill them while they're in the action of stabbing you it's self-defense, but if a few minutes have passed it's murder.
If someone has made their intention to kill you clear, self-defense is a valid response, no time limit, no need to wait for triggers to be pulled. This is a group of people making their intentions clear walking down the street.