That’s quite a bit later than I expected, or should I say hoped it would air, but still not to look a gift horse in the mouth, mark your diaries for Sunday November 23rd.

The TV guide article revealing the date has a few more details about the prequel.

… Filmed partially on location in South Africa, the “prequel” finds Jack Bauer battling an international crisis (yea!), while back home, the United States prepares to inaugurate a new president.

“We’re excited about the prequel because it explores Jack’s complex emotional state of mind and still has all the signature excitement and suspense that fans have come to expect from 24,” says executive producer Howard Gordon. “Shooting in South Africa affirms everyone’s commitment to making this season especially memorable for our fans.” …

source : community.tvguide.com