Board Thread:Club Penguin Facts/@comment-4018164-20140812175651/@comment-25396835-20140812201937

Narrowed it down a bit: It seems to be between December 24th 2013 and January 21st of this year. Sources:

https://www.youtube.com/watch?v=X6LeaKfAwYw

https://www.youtube.com/watch?v=H8I29P8eiio