18 April

18 April was a date.
In 1906, the Earth city of San Francisco was ravaged by an earthquake and then consumed by fire. Thanks to the Seventh Doctor's interference, the gateway through which the creature Azathoth and her rakshassi army hoped to invade Earth opened not in the India of 1887 but in the lobby of the Palace Hotel. Azathoth and her followers were consumed in the fire, while the Doctor, Ace, Bernice Summerfield, Sherlock Holmes and Dr Watson escaped. The Doctor departed for England to retrieve his TARDIS, materialising in San Francisco mere moments after he left his companions, although the trip to England took three months. Holmes and Watson rejected the Doctor's offer to join him in his travels. He returned them to Baker Street in 1887. (PROSE: All-Consuming Fire)
In 2011The Doctor later shows Craig a newspaper dated 19 April; this was one day previous., the Eleventh Doctor visited Craig Owens in Colchester, and met his new baby Alfie. As he left, he noticed power fluctuations, and decided grudgingly to stay one more day. (TV: Closing Time)
In 3760, activists formed a movement known as the Slumber Party, to ban the Morpheus pods responsible for the Triton Sandman outbreak. (PROSE: Time Traveller's Diary)