I think they’ll definitely take their time at it; for one thing, there’s still Fox films that have been filmed (Deadpool 2, Dark Phoenix, New Mutants) and in development (Gambit, X-Force, Deadpool 3, New Mutants sequels, an X-23 film, the James Franco Multiple Man movie, the Kitty Pryde movie that Miller and Bendis are working on), etc. Likewise, Marvel’s got the rest of Phase 3 (Infinity War, Ant-Man and the Wasp, Captain Marvel, Avengers 4) and Phase 4 (Spiderman Homecoming sequel, Guardians 3, the Black Widow project, etc.) in the works.
So I don’t think you’ll see any integration until after 2020, which means that Feige and his crew will have some time to figure out how to integrate the X-Men into the MCU. Hopefully that allows for a smooth entry.