26 September

26 September was a date.
In 1905, Albert Einstein published his special theory of relativity, paving the way for the first human time travellers. (PROSE: Time Traveller's Diary)
On an unspecified date in 1986, the Twelfth Doctor dropped Gertie off on Earth, promising to return on 26 September. She waited 30 years until 26 September 2016, when he finally returned. (COMIC: Super Gran)
In 2016, started working at Saxon Heights. (PROSE: Yes, Missy)