It's not how long there is between the incidents, it's whether or not the law sees them as being distinct.
Generally speaking, if a person disengages and genuinely tries to escape and is prevented from doing so or is pursued and attacked, then that will likely be viewed as a separate incident and the pursuer/attacker will be the aggressor/offender in that incident, regardless of how the initial incident started or who was the offender in that incident.
For example, Bob tries to kill Frank. They fight and Frank gains the upper hand after about 10 seconds. Bob now breaks away and runs. Frank chases him down and catches him a couple of seconds later and begins beating him.
The fact that Bob tried to kill Frank gave Frank justification for defending himself with as much force as was necessary to stop the attack. But once Bob broke off the attack and ran, Frank no longer needs to defend himself. That incident is over and there's no lasting justification for Frank to use force against Bob.
The key here is that justifiable use of force/deadly force is about prevention. It's not justified for revenge or punishment (those are things that happen after the fact and after the fact justification no longer exists) it's about stopping an attack in progress or one that is imminent (those are things that are happening or are about to happen).
Once Bob runs, there's no longer any need for prevention. The attack is over, there's nothing to prevent.
But Frank chose to pursue Bob and attack him. The law will very likely see that pursuit and attack as a separate incident even though it happened only a few seconds after Bob's initial attack on Frank. Because Bob genuinely tried to get away, the first incident ended at that point. The second incident consists of Frank pursuing and attacking Bob.
On the other hand, if the fight continues more or less without interruption, as long as Bob is still engaged, Frank can continue to do whatever it takes to prevent Bob from killing him. Even if the attack goes on for a long time, as long as Bob is actively and potentially effectively trying to harm Frank, Frank can keep fighting back. The fight could go on for 10 minutes and Frank could still have legal justification for defending himself with deadly force because Bob is still pressing the attack.
One concept that people seem to have difficulty with is the "Myth of the Good Guy." This is the same thing as "The Myth of the Bad Guy."
The Myth of the Good Guy is the idea that in a situation there must be a good guy. The good guy is intrinsically good and you can tell just by looking. Once the good guy is identified, you're done. You don't really need to do any more analysis because the good guy is, of course, in the right.
The Myth of the Bad Guy is just the other side of the coin. In a situation there must be a bad guy. The bad guy is intrinsically bad and you can tell just by looking. Once the bad guy is identified, you're done. You don't really need to do any more analysis because the bad guy is obviously in the wrong.
These are myths--they are false.
The fact is that the circumstances of the situation determine who's in the right and who's in the wrong. Not something intrinsic about the people involved. Not something that's immediately obvious by looking at the participants.
Since circumstances can change, that means a person can start off as the offender--as a criminal but could, before everything is over and done become the victim as circumstances change. Or a defender can start off with perfect justification and then as the circumstances of the situation change, end up as an attacker--a murderer.
It's important to understand this fact. Just because you start off a situation as the good guy, as the victim, doesn't mean you keep that status indefinitely. You can overstep your justification and become the bad guy, become a criminal. We saw this happen in the Jerome Ersland shooting where he justifiably shot a criminal who attempted an armed robbery at his pharmacy but then reloaded his gun and executed the robber as he lay helpless on the floor. He started off as the good guy, the victim, but then became the bad guy--a murderer.
Even though the two incidents happened with only seconds separating them, the law viewed them as very different. In one, Ersland was the victim, legally defending his life against a deadly threat. In the second one, Ersland was a murderer. He still looked the same, he was still the same person, but the circumstances were different in the second incident and that changed everything.
In the same way, the robber started out as the attacker--an armed felon, but ended up as a victim when circumstances changed.
