LONDON - Christian Marclay's "The Clock" is both the ultimate feature film and an artwork you can set your watch by.

The Swiss-American artist has edited together thousands of movie clips containing clocks, watches or references to the time - one or more for every minute of the day - into a 24-hour video.

The result is a mesmerizing patchwork that moves forward in time as it dances back and forth across film history.

Marclay compares the three-year process of creating "The Clock" to slotting together the multicolored facets of a Rubik's Cube. London's Tate Modern , where it goes on display this week, calls it "a gripping journey through cinematic history as well as a functioning timepiece."

Since it was completed in 2010, "The Clock" has taken on legendary status, watched by thousands of people around the world - including a hardcore few who have seen it all in one sitting.

Marclay knows most visitors won't see the whole thing, and admitted Tuesday that he's never sat through the full 24 hours.

Christian Marclay's 'The Clock' is both the ultimate movie, and an artwork you can set your watch by.

"It's a lesson for life - we can't do everything and we can't see everything,'' the artist said at a preview of the exhibition.

He likened the work to a painting - "You can come back to it endlessly."

Tate co-owns a copy of "The Clock,'' one of six in existence, with the Pompidou Center in Paris and the Israel Museum in Jerusalem.

Marclay places strict conditions on how it is shown. It must always be synched to the actual time, so that midnight onscreen coincides with midnight in the screening room.

Visitors to Tate Modern can see "The Clock" for free from Sept. 16 until Jan. 20, in a screening room that can sit 150 people on comfy couches. Tate plans several all-night openings so that it can be shown in its entirety.

While few viewers of "The Clock" last a whole day, many stay longer than expected - the average is more than an hour.

It's a seductive work that engages viewers on several levels. There's the fun of trying to recognize the snippets as they whiz past - Jack Nicholson smirking; Cary Grant flirting; Hugh Grant, late for one of his "Four Weddings and a Funeral."

Although there's no plot, "The Clock" contains sex, humor, action and dramatic tension. When Jeremy Irons calls Bruce Willis at 10:50 a.m. in "Die Hard With a Vengeance" and demands he be downtown in half an hour, viewers hope Marclay will cut back to Willis at 11:20. (He does).

Christian Marclay's 'The Clock' is a mesmerizing patchwork that moves forward in time as it dances back and forth across film history.

The artist says some minutes of the day were easier to work with than others. Film history abounds in noon and midnight encounters, but not so many at 4 a.m.

Only the insomniac or the intrepid will get to see the pre-dawn segments, and Marclay doesn't mind if late-night visitors nod off. He says he wants "The Clock" to be in synch with viewers' body rhythms.

"I love the idea of someone going in and out of sleep," he said. "It becomes a blur. You really become part of the thing.

"I think that's the magic of this piece," he added. "It's really about you."