Around the end of February 2017 the developers introduced a new type of timed quest challenge.
We refer to these as Timed Expansion Challenges or TECs. These challenges are tied to different expansions, and are prompted by a player opening that expansion area. Also, if a player has that area opened before the challenge is introduced, they will automatically be prompted to do the challenge.
Note: Both columns may be sorted alphabetically by using the arrows next to the column title. If you know the area you want to open, you can search for it easily.