I watched it years ago, and I didn't remember much of it, but I still thought I'd be able to follow it better this time.
Instead I was like "Ok...ok...what? Oh I remember now. Ok... shite I give up."
What helped me was this: Image: http://www.terminally-incoherent.com/blog/wp-content/uploads/2008/08/644px-time_travel_method.jpg
SO - time travel becomes sort of a proxy for Camus' concept of the only willful decision most of us make is whether or not to commit suicide.
Then, the rest of the analysis becomes when the time travelers break the rules, as they become more powerful and confident, each trying to secure position over the other, while simultaneously trying to correct mistakes/errors/unintended consequences along the way.
I won't paste it here because it's massive, but another chart that helps visualize something that is intrinsically difficult to visualize. LINK
Hope this helps, at least a little. As a film, I think it is very clever. Just enough science in it to appear plausible.
This post was edited on 2/4 at 3:33 pm