Originally Posted by Super Jim
My point is that there isn't just "one present". That kind of defeats the whole idea of Days of Future Past.
Except it doesn't.
The movie can still work with someone travelling to 1973 to do something which can prevent a horrible future.
The film may keep the part where something in the past has changed, which then causes this horrible future. But they may not.
The very last thing the movie is going to do is return to "Present 1" - the post-X3 timeline - by the end of the film, when the decisions made in that film are the "****" Bryan wants to fix.