At 20 minutes each way you're looking at about 160 hours of extra driving over the next 12 months, what dollar figure do you value your free time at? If it a fairly conservative $10/hour, that's $1,600. Lets say the commute is 10 miles and your car runs at $0.30/mile. You're going to drive 4,800 miles at a cost of $1,440. So the total cost of your new commute for 12 months would be approx $3k, or $250/month.

Now look at how much it costs to break your lease and move. My personal cost to do this would be 1k, I have no idea what yours is but plug in your own number. Subtract, and the cost of staying over leaving is an additional 2k. For every month you stay, subtract $250 from that savings (so decide quickly if you get an offer!).

Personally I would move within the first few months, as long as the job is what I expected. Those few months give plenty of time to check out the area around work and decide exactly where to live. My reasons for moving are partially financial, but also the practicalities of being close. I like to go home for lunch sometimes, to go several days in a row without getting in to a car, and getting a little exercise each morning and evening. A car commute makes those things difficult.