13 hours if you don't stop.. but i'm sure not all the roads are clear and many grown over.
Also no gas stations to refuel, unless he used multiple vehicles or had a big ass gas tank.
Lastly, people on the way would be like WTF a working car? and try to stop and get a hold of it. (kind like the Tom Cruise movie War of the Worlds)
As far as the Walking Dead there should be plenty of gas because the living polulation is not there to use it all, unlike Revolution, where there is a population sure, they can't use it for cars but you have to figure it's pretty scarce because people would use any flamible fuel they can find to heat powerless homes and buildings.