Originally Posted by Scaeva
Lee was out for two days.
We know this because Clem survived on her own for two days before Lee stumbled upon her house, and zombies had had not overrun the city before Lee was being transported to the prison.
The cop transporting Lee has no reaction to the police cars and helicopters speeding in the other direction, the radio chatter in the police car is confusing zombie attacks for disturbances and the like, and the transporting officer doesn't have a care in the world. He even shuts the radio off at one point because it was interrupting his conversation. He was obviously oblivious to what was going on.
The outbreak occurs while Lee is being transported, not before.
I've seen more than a few theories claiming otherwise. These theories speculate that, in other zombie related films/comics/books etc. (they named a movie where this happened but I can't for the life of me remember which film it was) the main character didn't encounter the undead until several days after the beginning of the outbreak. Please explain how the cop was being ripped apart and screaming for two days, then, without dying. Shaun certainly didn't take too long.
Then again, these ARE of course, just theories, not facts, so you may well be right.