NBC’s The Sing-Off is doing so well in the ratings that the network’s decided to expand the December 20 season finale by a half-hour.  But here’s the really exciting news: The Peacock plans to use the Sing-Off finale as a platform to promote the new midseason sitcom Perfect Couples.  Following the finale a “preview episode” of Perfect Couples will air from 10:30PM to 11PM; the network makes it clear that this special preview is not the pilot. That will be saved for the show’s true premiere date set for Thursday, January 20 at 8:30PM.  It will follow Community in the Thursday night comedy block, which was recently extended to include six shows in total.

Perfect Couples follows three couples at various stages of their relationships.  Here’s a quick synopsis: Dave (Kyle Howard, My Boys) and Julia (Christine Woods, FlashForward) are the relatable, normal couple, but Julia’s hope of remaining the cool, low-maintenance chick is tested by Dave’s attempts to keep both his wife and his needy best friend Vance (Dave Walton, NBC’s 100 Questions) equally happy. Vance, along with the neurotic Amy (Mary Elizabeth Ellis, It’s Always Sunny in Philadelphia), are the high-passion, high-drama couple who bring out the best and worst in each other.  The third duo features Rex (Hayes MacArthur, She’s Out of My League), a reformed party guy, and his wife, Leigh (Olivia Munn, Attack of the Show), who considers herself as the group’s mother hen. Believing that they are relationship experts, Rex and Leigh have attended every class and seminar on relationships — and regard themselves as the ‘perfect couple.’”

Update: Well there’s been a change in scheduling here, so take note: The Sing-Off finale will remain two hours in length, and the Perfect Couples preview episode will air at 10PM followed by a repeat of The Office.

[Via Deadline, here & here; EW]