Time travel is a curious science, more so in what changes could and would be made when travelling backwards in time rather than wether it actually is possible.
    In the classic "Back to the Future" (spoilers ahead) we see how Marty almost ends his own existence when through his interference his mother fails to fall for his father in the past. According to the Doc. he would himself disapear if he wouldn't be able to fix it. An interesting theory, but completely flawed. Why would he disappear, there's no reason for it, he was there, back in the past, and according to the laws of physics matter and energy can not simply seize to exist.
    In fact, doesn't the Chaos Theory prove that even if he hadn't interfered with his parents lives everything would still have changed? Think about it, life is a constant game of chance, what would the odds be that every die (die - dice, fig., not lit.) would roll the same way a second time around?
    In Startrek: First Contact (spoilers ahead) we can see how the Borg travel backwards in time and attack the Earth, how the crew from the Enterprise mingle with 21st century civilians. Again what would be the odds that when the crew return to the 24th century they would find an equal universe as the one they left when they followed the Borg sphere into the 21st century?
    So, if you travel an hour back in time, wouldn't there be two of you? In fact, couldn't you in theory create a whole army of yourself? Many hands make light work. Get a gun,  travel back in time, and have yourself do your bidding and then kill your (other) self. Kinda like Homer Simpson in that halloween episode where he cloned himself with his magical hammock.