TIme between kill and execution?

How long do I have to wait after taking damage from an enemy champ for a death to become an execution, because sometimes I run the wrong way, but don't want to give a kill, juking as I run, so I would decide to run into turret to get executed, but how long do I have to wait after receiving damage until my death can become an execution? Same goes with a chain of kills. Sometimes a player would get a quadra nd hunt down the 5th player, but how long does it have to be for the penta to not be eligible?