Two drug dealers/addicts get ahold of some crystals that, when smoked like meth, give them the ability to travel through time. While they mess things up ridiculously, they solve the problems by the end, even if it's not to satisfaction of anyone involved.
While there are som minor issues, this is about as perfect a time-travel story as you'll see. While the specific mechanism and rules are not mentioned, they aren't necessary. While there is plenty of time travel, no one leaves the room and there is minimal editing; you are actually able to follow one character's travels, and it shows both sides of a conversation she has with herself.
This is definitely well worth a watch, especially if you like time travel stories.
