Currently finishing up "X-Men: Days of Future Past," filmmaker Bryan Singer has confirmed that the film directly ties into the next film "X-Men: Apocalypse" albeit in ways you won't expect. Singer tells EW:
"You won't feel at the end of the movie that it set up Apocalypse. What it does is it sets up possibilities.
What we'll discover in Apocalypse is that events in this movie made that happen. Apocalypse deals with ancient mutancy. What would humans have thought mutants were? What would mutants think humans were?
You're dealing with gods and things like that. And what if one survived and what if that found its way into our world?"
Writer-producer Simon Kinberg adds that while 'Days' "necessarily create an alternate universe," it does allow some swapping of things which they are playing with. He also says "X-Men: Apocalypse" will be even more epic: "From a visual standpoint it actually may be a bigger movie than X-Men: Days of Future Past because there'll be disaster movie imagery, like the title would imply."
Finally, Singer added that he's keen to bring back younger versions of familiar mutants, such as Gambit and Nightcrawler, for the 1980s setting of 'Apocalypse': "I'm excited because I want to start introducing familiar characters at different ages and also explore the '80s."
Fox has also published an interactive timeline for 'Days of Future Past' which you can access at 25 Moments. The site explores 25 key moments in X-Men/mutant history from the Cuban Missile Crisis in 1962 through to at least 2018. Some little details are also included suggesting at least two major character deaths following the events of "X-Men: The Last Stand" and the near-future scenes in this film.