Update December 16: NBC has downsized The Sing Off finale back down to 2 hours, but will still preview Perfect Couples after. NBC will air a repeat of The Office from 10:30-11p.
Variety reports NBC is expanding the finale of The Sing Off by 30 minutes next Monday. The Sing Off finale will air from 8p-10:30p and NBC has slotted in an episode (not the pilot) of new comedy Perfect Couples at 10:30p. This bumps the Chuck repeat originally scheduled for 10pm.
Perfect Couples will still premiere in its announced Thursday, 8:30p slot on January 20.
NBC can't be faulted for wanting to take advantage of The Sing Off's better-than-expected ratings, both by extending it and using it as a lead-in for something other than a repeat.
NBC is also bumping previously scheduled Chuck repeats on December 27 in favor of a repeat of the TV movie A Walk in My Shoes.