Following the fall of Gallifrey, the events of the Last Great Time War between the Daleks and the Time Lords were contained by a time lock, thus isolating the conflict in its own specific timeline, (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) which was mostly separate from the normal universe. (PROSE: Revenge of the Nestene)
According to conflicting accounts, the time lock was placed by either the surviving higher species (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) or the Doctor. (COMIC: Don't Step on the Grass) This time lock was intended to ensure that no entity or faction could use time travel technology to revisit the war to alter or otherwise engage with any of the events that had occurred. Such interference was deemed too dangerous, likely to place the integrity of the Time Vortex itself at risk. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)
In one account of the end of the Time War, the Eighth Doctor, having used the Moment to destroy Gallifrey Original, tumbled out of existence as the Time Lock containing the war solidified, falling into plasmaspace, then foulspace, then beyond into infinity before he was ultimately retrieved by the TARDIS. (PROSE: Doctor Who and the Time War)
At the end of the Time War the time lock tore right through the planet Lujhimene, severing it in half. The time lock maintained the planet's gravity and atmosphere, and also spun its core as if nothing had happened. The Eleventh Doctor visited Lujhimene looking for the Volatix Cabal. (COMIC: Running to Stay Still)
Dalek Caan, the last survivor of the Cult of Skaro, was able to enter the Time War after initiating an emergency temporal shift, proceeding to rescue Davros from death at the hands of the Nightmare Child. Together, they emerged in the post-Time War universe with Caan being greatly affected both physically and mentally by the ordeal, appearing to have gone insane to observers. Knowing that the "entire war" was time locked, the Tenth Doctor proclaimed Caan's feat to be "impossible" whilst Davros himself deemed it "remarkable" that a "single, simple Dalek" had succeeded where Emperors and Time Lords had failed. (TV: The Stolen Earth)