Airlines cannot "fudge" flight data even if they wanted to. The actual "out" and "in" times are recorded and transmitted automatically when the wheel brakes are set off an on. These are the official numbers ("block time") reported to the DOT. UA also has another set of data, "off" and "on" times, for the actual takeoffs and landings. But I think those are just for internal use and don't appear in flight status.