Writers like to bring up big ideas and glaze over them enough to get the reader/view by. Sometimes it's done to keep the mystery and make it interesting (The Force). Other times, it's explained and then it loses its appeal, making it almost laughable (Again, The Foce - midichlorians).
In the case of M's ability, I feel it's at least semi-important to understand how it works. It isn't evident right now why it's important, but as the story progresses and M figures out more and more about his powers (at the same time the reader does) and certain events take place, his/your understanding of this "out of time" ability will be more important. To me, it's more fun that way. It's not as though I'm citing things prior to the books and giving the reader a slow trickle of info that I could have given from the first sentence, I'm giving it to you as the character figures it out. His experiences in the books are what demonstrate and build his understanding of his power. Sometimes accurately, sometimes not.
I'm not giving you every little detail with this blog posting, that would defeat the purpose of writing the way I am and take the fun away from you. I will give you the basic theory from the wiki and that will at least give you an idea of what us science fiction folk have been basing off of. http://en.wikipedia.org/wiki/Many-worlds_interpretation
I will say that the way I'm handling this topic is only shallowly based on this theory, but it's sill an interesting read that all of us know on some level because it's been used so much in books, tv, movies, etc.
Someday I should give my bs theory a name so that someone can post a wiki of it. :P