Kill streak timer

To set up my idea. I was playing mid, and was able to get a quadra kill in a team fight. Well the enemy was away from the team at the time. I tracked her down and killed her, but only got domanting instead of the Penta. I feel like we need a little timer like above your skill bar that will tick to show you when you are still able to get kills in a row. It would get shorter the higher your kill streak goes up, but I feel it would be helpful to know that you can tower dive to get the Penta (Which unless you are a tank you still will get killed) or when you notice that your window has expired and tower diving won't be the best option, cause you can't get the penta anymore. This is an idea, but I think it would be helpful in knowing when to risk for the penta or not.