Two dudes create box that acts as a time machine. Turn box on, get in it later and you can slowly go back to the point in which the box got turned on, but never before (obviously). Meanwhile, doing so creates an overlap of yourself and there are two versions of you running around until the point the first version of you (that turned the box on) gets into the box later, traveling back to the point where the second version of you got out of the box, extinguishing the overlap. Dudes build boxes, try to get rich while avoiding each other.
Dudes are having awesome adventures, decide that they want to go back and change an event, run into the VC guy who is now fucked from being in the box and can't figure out why he's there. This is when shit gets fucked. It's revealed that Abe actually build three boxes, turning the failsafe box on far earlier than the two they've been using up until this point and stashing it in another storage locker. Since this was turned on earlier, he can use it go back in time further and prevent the Aaron and Abe from the original timeline from ever getting involved in time travel and avoiding the whole situation with the comatose VC guy. He attempts to do so.
The box travel is exhausting and when Abe goes to meet Aaron to alter the conversation where he first told him of the boxes (after he had gassed himself), he passes out. And this is where shit gets really confusing and kind of convoluted. What I got:
-Aaron's headphones are replaying the recorded conversations from a previous timeline so that he doesn't deviate from it. The goal? Create a perfect timeline for his purpose without altering anything else.
-Aaron had discovered Abe's failsafe at some point. He moved it and essentially took control of the box which has been on the longest, thus taking control of the entire time traveling situation. I got a bit confused here, but it seems that he actually also moved another box back in time with him, using the failsafe. He uses that box to make a "fake failsafe" which Abe later uses. Actually, the whole mechanics of this and why (beyond the simple "so Abe doesn't suspect") throws me off. It's kind of a cluster fuck, but Abe doesn't make it back as far as he would like.
-Aaron has been traveling back a lot. He drugs himself, takes over his own spot, and throws himself in the attic. Yet another Aaron shows up, they fight, and 2nd Aaron beats 3rd Aaron (presumably because 3rd Aaron had traveled back further). They talk it out, one Aaron sticks around, the other disappears, and the third is in the attic. Which one stays and which goes doesn't really matter as we can probably assume that the conversation they had served the same purpose as having the third stick around - whatever was going to be done was going to be done. This is confusing as fuck. Especially because Aaron's motivations are never explained.
-Eventually Abe 2 and Aaron 2/3 (maybe more?) intersect at the point on the bench where Abe goes down. That's the point things get really confusing because the narrative shoots through and explains some of the events above, really briefly. What we can assume is that Abe 2 and Aaron 2/3 are more or less on the same page at this point. Begrudgingly.
-They do their thing. Aaron 2/3 disappears. Aaron 1 gets out of the attic and resumes his normal life. Abe 2 sticks around and tries to prevent Abe 1 and Aaron 1 from building the machine (or using it further? That would make more sense considering the timeline of the party).
Great. But the things we don't see are probably the most important as I see it:
-After the building of the box, I don't think we've ever seen the "original timeline". After that point, we're probably seeing different variations of Aaron and possibly Abe (although it could still all be Abe 1 going through his first run).
-Something that happened in the original timeline provided Aaron with his motivation, but we never actually see it. The weirdest part of the movie is why he's so caught up on this game, and that's the biggest indication that we haven't seen the original timeline. Chances are that Rachel died at the party, or at least SOMETHING bad happens with the shotgun toting guy. Hence Aaron's motivation to use the failsafe to go back, rather than just being a fucking weirdo. And whatever it is, it takes more than one try to get right.
Of course, there are some pieces that don't fit or aren't explained as far as I can see it. The time traveling VC guy doesn't serve much purpose rather than to serve as a catalyst to Abe using the fail safe and discovering that Aaron has been hopping around and also that other timelines now exist. I'm sure, however, that there's a deeper meaning to this. Likewise, the narrative phonecall from Aaron probably has more weight to it than just being a convenient explanation, and finally, the scene at the end with Aaron 2/3 in a foreign country building something (giant box?) must play in somehow.
That said, good movie, and surprisingly actually confusing as fuck the first viewing.