- This is an article about the general theme pertaining to the show. For specific dates of events referenced on the show, see Timeline.
The Rolex watch. ("House of the Rising Sun")
The passage of time was a recurring theme in Lost. Characters traveled in time coming and leaving the island, and skipped randomly through time over a series of episodes. Time also serves as a general recurring motif, with frequent references to time and appearances of clocks and watches.
Lost consistently played with time by presenting events out of their chronological order. Initially, action alternated between current events on the island and pre-crash flashbacks. Later episodes featured extended flashbacks and flashbacks to on-island events. "Through the Looking Glass" and Season 4 featured flash-forwards, and physical time-travel occurred in Season 5. In the final season, action alternated between on-island events and events from the characters' afterlife. Characters have also often experienced premonitions of future events. According to Damon Lindelof, LOST "has always been a little bit of a time-travel show" because of this non-linear storytelling. 
Desmond wakes up in a military barrack in 1996. ("The Constant")
The show first hinted at time travel in "The Long Con." Desmond's consciousness traveled through time in "Flashes Before Your Eyes" and later, more explicitly, in "The Constant." In the following season, characters and the entire island travel physically through time.
Time on the Island
At Comic Con in '06, the following fan question was asked and answered, somewhat obliquely:
Fan 4: Do you guys have any idea of how long, for the entire series, how many days it’ll take place in?
Carlton Cuse: You know, days? We never actually counted days. I mean, by the end of the show, hopefully we’ll have covered a lot of history, going back and forth… I mean, obviously, we saw that statue, that statue is kind of old?
Damon Lindelof: At least 50 years old. [Crowd laughs]
Carlton Cuse: At least… And probably, a little older?
Damon Lindelof: Maybe, maybe.
Carlton Cuse: And that was sort of… that, that was a signpost that the history of the Island may be a lot of um… more extensive than we’ve already dealt with on the show… so I think, by the time the show is done, we’ll have covered a lot of time. And um… in terms of how many days on the Island specifically, I dunno? 117?
Damon Lindelof: It’s interesting that you should ask about time because… you know… you’re making a basic assumption that they’ve been there, y’know, as long as they think they’ve been there. [Crowd murmurs, someone says “Oh, no.”] I would say by the end of Season 3… that very different idea…
Carlton Cuse: Stop right there, Damon, stop right there.
Damon Lindelof: Well, I was just…
Carlton Cuse: Stop right there. Nope, nope, no.
In an interview, Cuse also dropped additional hints about the significance of timelines (Entertainment Weekly):
Interviewer: What is the meaning or significance of the two skeletons that Jack and Kate found in the cave of season 1?
CUSE: The answer to that question goes to the nature of the timeline of the Island. We don't want to say too much about it, but there are a couple Easter eggs embedded in [ Not in Portland ], one of which is an anagram that actually sheds some light on the skeletons and hints at a larger mythological mystery that will start to unfold later in the season.
Charlie says the survivors are "positively made of time" soon after the crash, and Michael later says "time doesn't matter on a damn island." ("Walkabout") ("House of the Rising Sun") Richard tells Juliet she's "gonna be amazed at how time flies" on the island. ("Not in Portland") When Colleen dies, Jack can't find a clock to mark the time of death. ("Every Man for Himself")
Time on the Island appears to pass differently from time elsewhere. In experiments, objects traveling to and from the island have arrived at unexpected times, suggesting either time dilation or time travel. ("The Economist") ("Eggtown")
Clocks and watches
Countdown timer in the Swan station
Clocks form a recurring motif within the show. Mr. Paik sends Jin to deliver a Rolex watch, and Christian gives a Jack an heirloom watch in the mobisode called "The Watch." The Swan's countdown timer appears throughout Season 2, and alarm clocks appear in several scenes as character wake up. ("Exodus, Part 2") ("Two for the Road") ("Because You Left") Ben consults a watch to see when to kill his father, and years later, he uses another to decide when to order Sayid, Jin and Bernard's deaths. ("The Man Behind the Curtain") ("Through the Looking Glass, Part 1") Sent back in time, Desmond glances at a clock then visits Mrs. Hawking, whose shop is full of clocks. ("Flashes Before Your Eyes") The temple uses a large hourglass. ("LA X, Part 2")
Other references to time
- Locke tells Walt: "Backgammon's the oldest game in the world. Archeologists found sets when they excavated the ancient ruins of Mesopotamia -- 5,000 years old. That's older than Jesus Christ." ("Pilot, Part 2")
- Sayid tells the group that the distress signal has been repeating for "16 years and 5 months, that's the count." ("Pilot, Part 2")
- Charlie updates the bandages to say LATE instead of FATE and the camera scans to Claire's belly. ("Tabula Rasa")
- Charlie tells Locke that he hasn't played his guitar in "Uh, 8 days, 11 hours, give or take." ("House of the Rising Sun")
- Jack remarks about Adam and Eve's tattered clothing: "It takes 40 or 50 years for clothing to degrade like this." ("House of the Rising Sun")
- Boone asks Locke whether they will be working on the Hatch for 4 months like Michelangelo on the Statue of David. ("Hearts and Minds")
- Locke remarks about the clothing on the skeleton in the jungle: "Normally clothing would completely decompose within 2 years, but this is high quality polyester -- could be 2 years, could be 10." ("Deus Ex Machina")
- Kate's time capsule is her driving purpose in several of her actions as a fugitive. ("Born to Run")
- Hurley says, "Twinkies keep for, like, 8000 years, man." ("Exodus, Part 2")
- Hurley nearly missed the plane because the alarm clock in his hotel room stopped working. Explaining this to an Oceanic Airlines employee, Hurley says "I don't really get the whole time change thing." ("Exodus, Part 2")
- Jack says, "I've got time." ("Man of Science, Man of Faith")
- Locke organizes shifts of 6 hours to stay in the Swan. ("Everybody Hates Hugo")
- The title of episode 7 is "The Other 48 Days".
- Ana Lucia tells Goodwin: "This knife's probably 20 years old. You don't see these anymore, yet here it is, on this island. Weird, huh?" ("The Other 48 Days")
- Michael was given three minutes with Walt; this was also the title of the episode. ("Three Minutes")
- Desmond tells Claire: "You're wasting your time, sister. I shot myself with that stuff every 9 days for 3 years." ("Live Together, Die Alone, Part 1")
- Ben asked Jack for "3 minutes" since he had only "27 minutes to live". ("Not in Portland")
- Juliet gives the exact length of her stay on the Island: 3 years, 2 months and 28 days. ("Not in Portland")
- The company name Mittelos is an anagram for "lost time". ("Not in Portland") This was confirmed as being the plot-significant anagram to look out for in the 2/12/07 podcast.
- The company that made the red paint that Desmond was using to paint the walls of his flat with was called "FUTURE" paint. ("Flashes Before Your Eyes")
- Kronos is a fictional company shown in an Easter Egg as an ad in the TV soccer game Desmond is watching. Kronos is a titan in Greek mythology, generally regarded as the god of time. ("Flashes Before Your Eyes")
- A Brief History of Time - Non-fiction book about astrophysics and theories on how the universe began (seen in Lost)
- Watchmen - Graphic novel/comic book series that features a character who experiences time in a non-linear fashion (confirmed influence on Lost)
- A Wrinkle in Time - Fictional book on time travel through tessaracts (seen in Lost)
- Slaughterhouse-Five - Fictional book with a protagonist 'unstuck' in time
- The Chronicles of Narnia - Fictional book where there is a time difference between Narnia and the real world