"Rules - You can't have time travel without rules, see every other show or film based on time travel, start messing about and it becomes stupid."
On the contrary, no set of time travel rules has ever made any sense. There is no getting round the grandfather paradox. If you're writing a time travel story and you get hung up on "rules" all you are doing is storing up trouble for yourself - the plot holes just get bigger and bigger.
Mostly time travel stories are just a variation on the "prophecy" plot device that has been around since ancient Greek theatre. We know what's going to happen and the drama is in finding out *how* it's going to happen.