These are good questions, and Singer seems to be looking at time travel with this...dilemma in mind.
At the Fantasia Film Festival he had this to say
(my transcription might be a little off):
Q: Time travel has always been a staple of science fiction. What are some of the pitfalls in working with the time travel sub-genre?
A: Well, it was tough to crack. It took me a little while to figure out what my rules of time travel are, and um, there are movies that--Especially a movie like Back to the Future, it really all takes place in the past, and your one grounding element is this photograph that keeps fading. So it's trying to find a device like that for a movie that has things happening in the past simultaneously with what's happening in the future. So I won't get into the specifics of it but I sort of came up with a formula of how it would work and then I adhere to it, I stay true to it.
Originally Posted by CyclopsWasRight
Perhaps Xavier and Kitty while linked to Logans mind are outside of time with the events of their time changing around them. This would however have the rest of the OT cast change around them.
That's not a bad idea.