These guys build a device and figure it that it's a time machine that sends you back for 16 hours or so, but it actually only sends you back for a fraction of a second and makes a duplicate of you at the same time that is sent back 16 hours previously?

The two guys build a device and figure it that it's a time machine that sends you back to the moment it was turned on. The amount of time backwards you travel is equal to the amount of time the machine has been on, and takes the same amount of time to travel backwards, e.g. a machine turned on for 8 hours will send you 8 hours into the past and will take 8 hours sitting in the machine to do so.

After Abe, the blonde-haired guy, reveals this to Aaron, the brown-haired guy, Aaron stops a possible assault on Abe's girlfriend by an ex at a party. Abe finds out about this later. This is an important plot point that doesn't reveal itself as such until later.

The guys use this at first to travel 8 hours back in time to the beginning of the day. What they do is first isolate themselves spend 8 hours doing nothing. Then they look up stocks and pick the strong performers that day. Then they spend 8 hours going back in time. They then proceed to buy the stocks they know will perform well that day and take the profits at the end of the day. The machines are one-use only, meaning that you can only travel back to a certain point one time, although you can start them up again and create a new past point to travel to.

Everything is going smoothly until Aaron, the brown-haired guy, suggests hitting his boss and then going back in time to prevent himself from hitting his boss, which would create a paradox. Abe, the blonde-haired guy, is adamant that they avoid paradox. Still, the idea has been planted.

One night, Abe is awoken by someone setting off car alarms. He calls Aaron, who comes over. Abe has been turning on the machines around 5pm to let them run all night before they are turned off and turned on again in the morning for their daily routine. So they can go hit Aaron's boss, go back to 5pm and then proceed to stop the kid from setting off the alarms, thus not waking Abe and causing him to decide to go back in time.

However, on their way to do this, they notice that Abe's girlfriend's dad, Thomas Granger, is following them with a 3-day beard. Mr. Granger is a businessman they've previously tried to persuade to invest in their company. Suspicious, they call his house. Thomas Granger is at home, so they know the Thomas Granger following them is from the future. They try to confront the future Thomas Granger, who flees and then collapses. Unsure of what to do, Abe decides without telling Aaron to use the fail-safe.

The fail-safe is a third time machine that has been running since before Abe first traveled back in time, and since before Abe told Aaron about the time machine. Abe has never told Aaron about this backup device. At this point, going back in time requires several days in the machine, so supplies of water, food, and drugs are needed to make the trip.

Abe travels back and starts to redo the conversation that he had with Aaron at the park bench when he told Aaron about the time machine. However, Abe is weak and collapses. This is where it gets complicated. It's at this point it's revealed that Aaron has also travelled back in time, and multiple times at that, since he has a tape that has all their conversations recorded on them, so that he can recreate them perfectly. Aaron found out about the fail-safe and used it as well.

So, if the machines can only be used once, and there was only one fail-safe, how did Aaron come back? This is where the movie reveals the "box-in-a-box" concept, where Aaron brought a time machine back with him inside the time machine he traveled back in. Thus he was able to create a second unused time machine that comes back to the same point as the fail-safe. Basically, this means that the one-use only rule is out the window, they can go back to the same point in time as many times as they want.

Now here is where recursion kicks in. The Aaron on the park bench, and in fact the abe through most of the film, has been Aaron2, from the future. Aaron2 traveled back almost as soon as he found out about the machine. The reason he was able to stop the assault at the party was because he knew that the assault would happen, although he also knew the ex doesn't actually go through with the assault. Earlier in the film, Aaron's wife complained about noises in the attic, we now know that it was Aaron1 up there, who had been put there by Aaron2 to be out of the way.

Now, remember the narrator? It sounds like Aaron, but it's actually Aaron3. Aaron3 came back and tried to overcome Aaron2, but Aaron2 fought him off, and Aaron3 left, to never return. Up to this point, everything the narrator has described is first-hand experience. After this, it's only what he heard.

Also, after this point, my understanding of motives and such get a little fuzzy. Aaron2 contrives to have Abe2 stop the assault at the party, presumably to put him in good with his girlfriend and her dad, Thomas Granger. Aaron2 and Abe2 then conspire to prevent Abe and Aaron from ever successfully making a time machine. Then the paradox hits in, in that Abe and Aaron never make a time machine and travel back in time, yet Aaron2 and Abe2 continue to exist. They both must leave, although Abe2 doesn't want to leave his girlfriend. Abe2 decides to stay behind and watch over the Abe and Aaron to make sure they never make the machine. Aaron2 bolts for good.

The movie ends with a shot of Aaron3 in a foreign country surpervising a massive project. It's specualtion, but from Aaron3's statement that nobody will ever be able to find him, it seems likely that he's building a massive version of the time machine.

There are plenty of other little touches and things that I haven't touched on, but that's the main plot, in a nutshell (in this case the shell of a really large nut)

I was under the impression that they went back over and over again so that the fight could be stopped. However, every time they did it they wanted to make sure that everything happened the way it was supposed to happen. Ala the time they were playing basketball. Then once the entire day was set up perfectly they had to do something that would prevent the guy from having a gun.

So that is why they were going back again. IMO, it was after they accomplish what they wanted is when they used the box that was set running from the very beginning.

Though I thought there was a reference that one of them had killed one of his "duplicates", but I was tired when I watched it and my brain was half turned off.

I agree, they do travel back multiple times, at least twice. Aaron2 after all has a tape recording of the whole day, something he wouldn't have thought to do when he first experienced the day before time travelling. Aaron3 in the narration suggests the possibility of many more times, although it's conjecture for him how many more times. Also, I don't think they wanted to prevent the ex from having a gun, but to prevent it from being loaded. They wanted to give the appearance of being heros.

One great bit I liked from the basketball scene was how the conversation drifted from the previously recorded version when Aaron misses the shot, which he made previously, although the outcome of the conversation stayed the same.

The fail-safe was the only machine that went back far enough to affect the day they kept reliving. The other two machines had been used and reset before Aaron figures out how to get multiple uses out of them. However, once Aaron figures out how to keep going back to the same point repeatedly, the fail-safe is a bit of a moot-point.

There definitely are "duplicates" by the end of the film. However, this is more of a side-effect of paradoxes created by time travel than the expressed purpose of the machine.

In their initial stock market plan, they take great steps to insure that when they travel into the past they don't affect their past selves. That way, they don't prevent their past selves from becoming their future selves.

However, at the end, they travel back and directly affect their past selves and their lives. Therefore, they've changed the reason they came back, and their past selves do not correctly progress to becoming their future selves. This creates a paradox. In some films, this paradox is resolved by having the future self dissapear, as Marty McFly almost does in Back to the Future. In this film, the future selves continue to exist, essentially making them duplicates.

I don't recall either of the guys killing a duplicate version of themselves, although they both do subdue and lock up their original past selves to temporarily assume their lives. Also, one future Aaron, Aaron2, has a fight with an even furthur future Aaron, Aaron3, although Aaron3 actually loses and leaves, unable to achieve what he came back to do.

And the reference to why they can write correctly anymore, does this have to do with them being duplicates or that they have changed their pasts and created the paradox?

they were talking at the fountain

how many days have passed since they first went into the machines? because, if i understood the movie correctly, that's exactly the amount of time they have to spend in the machine each time they go back. and i don't think one could stay long in a machine like that

I don't think it has to do with them being doubles. For example, their original stock market scheme created a period of doubling up where there were two versions of them during the day: a past one hiding in a hotel, and their future versions buying stocks. This doubling resolved itself when the past selves would eventually travel to the past to become the future ones. Its only when they create a paradox where their past versions don't become their future selves that the doubling becomes permanent.

So the act of creating a paradox is what causes changes, and possibly their afflictions as well. One of them mentions that the Mr. Granger from the future can't get near one of them without passing out, which may be because of the paradox of his trip backward changing whatever caused him to come back in the first place.

Another theory is that the inability to write, the passing out, and the bleeding from the ear are caused by extended and/or repeated bouts inside the force field of the time machine. They do initiall describe the slightly odd feeling of being within the field, and the film also shows the ill effects of trying to exit the field when it's not at its weakest.

Each possibility has its drawbacks. The force field theory doesn't explain why Future Mr Granger keeps passing out. The paradox theory doesn't explain why Mr. Granger is so greatly affected while Abe and Aaron, who repeatedly create such paradoxes, are only lesser so.

It has been several days, about 3-4, although not a week. Before Abe makes his trip back through the fail-safe the narrator explicitly says how long it's been. To make that initial trip back, Abe uses medical equipment to induce a hibernative like state while keeping him hydrated and monitored. Basically, he just slept all the days back, with only a minimum of food and water. No wonder he looks so beat up when he makes it back. Aaron has been making trips back since the end of Day1, so he hasn't had to travel so far.

After each one's initial trip back to the beginning (when the fail safe was first started), each subsequent trip needn't had been from their original points, but from whenever they decide to travel back again. This is probably a period of no more than 16 hours or so, since the main thing they're trying to change, the attempted assault at the party, happens during the first day