I thought the same thing, so imagine my surprise the next day when I learned that Tower 2 fell after 40 minutes but Tower 1, the first tower hit, stayed up for about an hour and a half total.
Of course, I have a different problem altogether as an excuse--"lost time"--I cannot account for the hour-and-a-half after the first collapse, and have no real-time memory at all of Tower 1 coming down. Didn't see it until the next day on television repeats, when it came as a real shock.
Six weeks later I still can't fill in the blank.