1310

In 1310, Mulberry saved Nyssa from falling to her death in Rhodes. Shortly afterwards, they were sent forward in time to Virginia in the Confederate States of America on 30 July 1864. (AUDIO: Renaissance of the Daleks)

Behind the scenes
In Renaissance of the Daleks Nyssa says she was in Rhodes in 1320, while the Doctor later says it was 1310. Given the Doctor has a better knowledge of Earth's history than Nyssa, and the fact the real life Knights Hospitaller took over Rhodes in 1310, as is depicted, 1310 is the most likely date for this to be set.