Real time
From Tardis Wiki, the free Doctor Who reference
Terry of Gallifrey was obliged to obey real time. As such, when he retrieved Susan Foreman from the aftermath of the 2164 Dalek invasion of Earth, he dropped her off in July 1964 since she had been traveling in the TARDIS for eight months since her disappearance in November 1963. (AUDIO: Whatever Happened to Susan Foreman?)