2164

2164 was the date on a calendar found by Ian Chesterton upon arriving in the 22nd century. He went on to suggest it looked like it hadn't been changed for some time and so it was unlikely to be the actual date. (TV: The Dalek Invasion of Earth)

Behind the scenes
2164 was exactly 200 years after the year of first broadcast of the TV story. This implies greatly that the events of the serial did take place on this year, although it cannot be confirmed in-universe.