Originally Posted by Kinky John Fowler
Even once you've stopped breathing you have about 5 minutes or so before your body starts to shut down (hence CPR which Lee was trying to do before that idiot decided to step in), so you are looking at 5 mintes at the very least before he would have turned. Kenny acting preemptively did absolutely nothing in terms of favouring the group.
We don't know that's when they turn however, it doesn't seem like 5 minutes for the guy at the beginning who turns though it's not clear when exactly he dies. Look at it from the perspective of the characters, they don't know when the transformation occurs, whether you actually have to be dead to turn (for all they know they could all be slowly turning it just speeds up when you die), and hell I doubt Kenny, Lily or Lee even know themselves how long it takes for the body to shut down.