With the fall of Celestia and the return of Nightmare Moon, Equestria was in anarchy. The only safe-haven was Ponyville, where Cadence and Twilight were building the resistance.

Fluttershy is under a mind control spell cast by nightmare moon. Cadence and Twilight both knew that they had to find a spell to break it or one to bring back Celestia.

They had one week before the total annihilation of Equestria.
By Midnight Nebula