The on-screen flight time is just that - flight time - from takeoff to roll out. (Though I'm not sure how to set limits speeds for this, or even if you can.) The flight history, on the other hand, measure from when you start moving to when you stop. Depending on your airport and taxi, this will usually be .2 to .3 more than the flight time, but could be higher or lower. Officially, "log" time goes from engine start for the purpose of flight to engine shut down. Again, usually this would be maybe .1 more than the history time.
So you have options. I just use the history time.