A Memorial Day holiday release really does makes more sense than its previous release date on July 18. According to one of The Daily SuperHero's sources Fox changed dates due to one reason and one reason alone... they did not want to go head-to-head with Marvel Studios.
Specifically, Fox did not was their next X-Men movie to release only two weeks prior to Guardians of the Galaxy. Even though Marvel's space film will be their newest movie property, the studio's track record with its films is impeccable.
So, instead, Fox pushed X-Men Days of Future Past up and it will hit theaters three weeks after Sony's The Amazing Spider-Man 2 is out. The latest X-Men movie will have a chance to dominate the Memorial Day weekend box office and then some. There is now a window of nine weeks between Days of Future Past's release and the next Marvel movie on August 1 (GotG).
Sounds like a strategic play by Fox. Will it pan out so X-Men Days of Future Past to earns more money? We'll have to wait and see about that.