This is one of those high-concept movies that you have to buy into from the beginning or opt out. Here's the premise: On some future earth, time is literally money. People live to age 25, and then they have one more year to go. Unless they can accumulate more time. Minutes, even years, are easily transferred from one person to another or from some electronic device to a person. It's better not to think about how this works. Everyone's arm also has a glowing clock that counts down the time. (But nobody has a cell phone. Go figure.) There's plenty of time to go around, but a population of immortals would cause a lot of problems. So everybody but the members of the upper crust has to die sooner rather than later. This makes it hard for anybody in the ghetto to get any extra time. Even five minutes is highly valued.
Will Salas (Justin Timberlake) doesn't like the system, and when his mother dies on the same night that he comes into 100 years of time, he decides to take action. The rest of the film is a cat-and-mouse chase after Will kidnaps Sylvia Weis (Amanda Seyfried), the daughter of a guy who has millions of years and is apparently in some kind of control of who gets them. Will decides to steal some time and give it away to break the system. The more you think about the plot, the sillier it is, unless maybe you want to read it as a metaphor for the current divide in society based on hard currency. Probably better just to go with the flow and have a little fun. Not a lot, but enough for a lazy afternoon. You have the time to spare, don't you?