I found this also a couple of days ago on a facebook group:

UPCOMING EPISODES

Episode 12: The Western Air Temple 
-Canada aired it Friday Dec 14th
-Nick plans to air this episode on Friday April 4 (NEW)

Episode 13: The Firebending Masters 
-Canada aired it Friday Jan 4th. 
-Nick plans to air this episode on Friday April 11 (NEW)

Episode 14: The Boiling Rock Part 1
-Nick plans to air this episode on Friday April 18 (NEW)

Episode 15: The Boiling Rock Part 2
-Nick plans to air this episode on Friday April 18 (NEW)

Episode 16: The Southern Raiders
-Nick plans to air this episode on Friday April 25 (NEW)

Episode 17: The Ember Island Players
-Nick plans to air this episode on Friday May 2nd (NEW)

Yes, there is a week pause before the 2-hour Finale

Episodes 18,19,20,21: Sozin's Comet: the Final Battle (Subject to Change)
-Nick added an episode for the Finale so 21 episodes in this book for this Season Finale
-Nick plans to air this episode on Friday May 16 (NEW)

With this new schedule, the Sozin's Comet Book (which releases May 20th) will be on-time with the tv 
  87:57, 16 March 2008