Each episode is supposed to take one hour of real time but in actuality, due to commercial breaks three minutes are gradually added to the timer during the show in the breaks. The last three minutes of air time are used for viewing commercials, station identification, and scenes from the next episode. Each episode general runs for around 43 minutes without commercials (slightly less in PAL territories).
At the power plant before Palmer's breakfast speech, Jack runs into old friend and Palmer staffer, Jessica Abrams. In conversation, she refers to mutual old friend Tracy Zigler, who had erroneously reported that Jack and Teri had divorced. Both characters are named after members of the production crew; Jessica Abrams (II) is the script coordinator, and Tracy Zigler is the script supervisor.
Dennis Haysbert was shuttling back and forth from the east coast to Los Angeles during the production of the first season, because he was filming Far from Heaven at the same time.
Paul Blackthorne who plays season 3 main villain, Saunders, originally auditioned for the role of Amador, another one of the season 3 villains. After failing the audition, his agent negotiated with the producers and managed to get the role of Saunders.
During the shoot for season 4, a special six-minute segment was shot for the US version of the season 3 DVD where Jack loses his job at CTU, an antagonist of season 4 arrives in the US, and Jack has an intimate moment with his new girlfriend. This did not appear on any of the other versions of the DVD released earlier in the summer, however it does appear on the UK and German DVD release. An extended version of this segment (as stated in the commentary by director Jon Cassar) is available on the UK DVD release of season 4.
Mandy is the longest running villain to appear on the series. She made her first appearance in the first three episodes of Season 1 working for Ira Gaines, and returned in Season 2's finale for a cameo appearance where she tries to assassinate David Palmer. She returns again for the last three episodes of Season 4. Mandy was also originally intended to appear in Season 5, but was replaced by another character.
Season 4: Writer/Executive Producer Evan Katz was such a huge fan of Australian music duo Grant McLennan and Robert Forster (II) of the band The Go-Betweens that he named the sinister corporation McLennan-Forster after them.
Two episodes are filmed simultaneously over a period of 15 days.
In season 2, Tony Almeida's ankle injury was added to the script as actor Carlos Bernard had really injured his ankle while playing basketball during a break in filming.
Harris Yulin, who plays the recurring character of NSA director Roger Stanton in Season 2, is not credited at all in the opening or ending credits. All recurring and guest stars have to share their credits on screen with one or two other actors, but Yulin wanted to appear alone on them. Because this was not possible, he decided not to be credited at all.
Partway through season 2, Kiefer Sutherland injured his leg while exiting his trailer, so a small scene was written in where Jack Bauer must pull a piece of shrapnel from his leg after a plane crash to explain Sutherland's limp.
During season two shooting, Elisha Cuthbert was bitten by the mountain lion who menaced her in one of the plotlines. Before shooting the scene the animal trainer suggested she "meet" the mountain lion before shooting, when she went to pet the mountain lion it bit her hand. She was taken to the hospital, treated for puncture wounds and was given a tetanus shot.
Nina Myers' fake passport shows Sarah Clarke's own married name (Sarah Berkeley), but not her birthday, which is in 1972 (the passport shows 05.05.1975).
Season 3. Whenever Jack goes into the holding facility which houses Salazar, at some point, he is picked up by security cameras. The legend on the video surveillance monitor at the guards' station shows constantly that he is being taped by camera #24.
Season 3. A Mexican airplane appears briefly during Salazar and Bauer's landing on Mexican ground. The logo on its side reads "Aeromexicana". The name is comprised of Mexico's two largest airlines "Aeromexico" and "Mexicana".
During Season 2, President Palmer takes a flight aboard Air Force One. Reportedly, the sets used were the same used for the film Air Force One and The West Wing's Air Force One shots.
All cast members are required to have their hair trimmed every five days.
SPOILER: Although the writers changed their plans on Chase Edmunds's fate, they had a deleted scene planned in which Chase gets killed while he was having his hand re-attached in the hospital
Gabriel Macht was originally offered the role of Jack's partner Chase Edmunds but the producers were so impressed by James Badge Dale's audition they offered him the role and promised Gabriel Macht a significant role in the next season. This never materialized.
Jack Bauer has a Bachelor's Degree in English Literature from UCLA and a Master's Degree in Criminology and Law from UC Berkeley. Kim Bauer has an Associate's Degree in Computer Programming from Santa Monica College. President Palmer has a Bachelor's Degree in Political Economy from Georgetown University, and a Juris Doctorate from the University of Maryland School of Law. Tony Almeida has a Bachelor's Degree in Engineering and Computer Science from San Diego State University and a Master's Degree in Computer Science from Stanford University. Michelle Dessler has a Bachelor's Degree in Computer Science from UC Davis. Sherry Palmer has a Bachelor's Degree in Sociology from Georgetown University.
Completing an entire season, including pre- and post-production work, takes ten and a half months.
In Season 3, Stephen Saunders demands that the President reveal some classified information, which would then be sent to him via a website. The website he mentioned is SylviaImports.com. This site was actually registered by Rodney Charters, the show's director of photography (and director of a couple of second season episodes). It contains the following text message: "A Big Thank-you from the crew of 24. Thanks for watching, we love making it for you, and yes, we did get picked up for Season 4."
In Seasons 1 & 6 there is a CTU character called Milo Pressman (played by Eric Balfour). There was a character called Milo Pressman, who ran a scrapyard in the Stephen King's story "The Body" in his book "Different Season's". The story was later made into the film Stand by Me (1986) in which Kiefer Sutherland starred.
The crew tried to keep all the cameras at eye-level to add an extra level of realism.
The knife Jack Bauer uses is a Microtech Halo III SA Satin Blade Front opener.
Roughly 25 hours of footage are edited into one episode of the show.