It has been 20 days since the infection started. Celestia has run away from Canterlot with Luna (whom she forced along).

Celestia: ...We need to get moving faster, sister.

Luna: ...We should’ve stayed and helped th-..

Celestia: They can handle themselves. OUR goal is to get to that safe place!

They're walking through the snow covered Everfree Forest, heading for that not plagued place...who knows where, besides Celes'.