I think it's supposed to be about two years time passed now since the beginning (definitely less than the time the show's actually been on).
And I noticed last week that some lawns are finally starting to grow out lol.
as far as the gas goes, my Scamp sat for a full 4 years after I bought my Stealth, and it fired right up after all that time. So on TV they can go forever :D.
p.s. does everyone watch Talking Dead too? -last weeks episode was great...for legs anyways;)