Time override was the "locking" of a TARDIS's co=ordinates. The Doctor's TARDIS experienced turbulence when the White Guardian used time override to send the Fifth Doctor to Striker's ship. (TV: Enlightenment)
The Tremas Master later forced the TARDIS off course, having "overrode the controls" as the First Rani surmised. The Sixth Doctor explained to Peri Brown that they were being maneuvered off course from Kew Gardens, the time co-ordinates remaining constant but their location changing to arrive in Killingworth. He put this down to "time distortion, as if there's a time machine nearby." (TV: The Mark of the Rani)