Time Warp

I flew home from Florida on Thursday. I arrived at the airport and the flight was listed as being on time. When the plane was not at the gate I realized that we would be a bit late. We were supposed to take off at 1:30pm and land at 4:30pm. We actually took off at 2:00pm and you would think that the arrival time would then be 5pm. Somehow we landed at 4pm. How did taking off late make us arrive early?