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)
There are definately practical problems with him getting there in 13, 15, even 20 hours based on some of the obstacles.
You have to wonder though, in the Revolution world without power- what shape the fwy system would be in for someone to travel solo down it and would people have thought to scavange the underground fuel tanks at gas stations when the cars don't run? Also, do those tanks keep gasoline viable for a long time and are they treated with those chemicals to last longer.
But I get ya - lots of, 'suspensions of disbelief,' for that roadtrip.
There are always the magical nanites to solve any problem.