Easter

Easter was an Earth holiday normally celebrated in either March or April

On Easter of 1996, seven-year-old Amelia Pond was praying to Santa Claus, asking him to send someone to fix the mysterious crack in her bedroom wall, not long before the newely-regenerated Eleventh Doctor crash down to Earth and met her for the first time. (DW: The Eleventh Hour)

Because it was a moveable feast, the Doctor had difficulty navigating his TARDIS to the correct date. The Tenth Doctor, however, was able to land on Easter 2009 in time enjoy a chocolate Easter egg and to save the Earth from an incursion of the Swarm. On this occasion, he also stated that he had been present at the original Easter and intimated that the events were at variance with what humans believed. (DW: Planet of the Dead)