Fox has had to adjust their upcoming film schedule a bit due to the injuries that Maze Runner: The Death Cure actor Dylan O'Brien suffered on set during filming. As a result of that shift, Fox released an updated schedule with some new release dates, and it included two new slots devoted to Marvel projects.
The first Untitled Fox/Marvel movie (via Deadline) has been moved back from January 12, 2018, to March 2nd, 2018, while the second Fox/Marvel film has been moved up from July 13th, 2018 to June 29th, 2018. One of those is most likely a Deadpool sequel, as that project has already been greenlit. As for the other film, though, it could either be the New Mutants project, the much talked about X-Force movie, or even another entry in the core X-Men franchise, which is rumored to be another take on the Dark Phoenix Saga.
Those won't be the only Marvel films in theaters either during that time. 2018 is a pretty packed year for Marvel Studios, starting with the heavily anticipated Black Panther film that drops on February 16th, which is nestled right in between the first untitled X-Men project's old release date and new release date.
It's closely followed by the Russo Brothers directed Avengers: Infinity War Part 1 on May 4th. After that, Ant-Man and The Wasp hits on July 6th, which might be why the second X-Project was moved up a week to June 29th. Having it hit right after Ant-Man and The Wasp is probably something the studio wants to avoid, especially if it doesn't have the brawn of a Deadpool 2 to bring audiences into theaters on name alone.