According to MakingStarWars, "sources in the theater industry" have received a release date of Dec. 13, 2018, for the untitled "Star Wars" film, which stars Alden Ehrenreich as the young smuggler. The movie had been expected to premiere in May 2018.
The fan site lists corporate paperwork with "release date is subject to change" as evidence as corroborating evidence that a calendar move could be in the works. Also, the only press material that contained a May release date was the announcement of directors Christopher Miller and Phil Lord. Those for announcing "Atlanta" star Donald Glover as young Lando Calrissian and Emilia Clarke as a new character used the vague wording, "The untitled Han Solo movie is set for release in 2018."
Disney originally announced "Star Wars Episode VIII" for release on May 26, 2017, before moving it to the current date of Dec. 15, citing the “extraordinary success of ‘Star Wars: The Force Awakens'” as the reason. Every franchise film before that had been released in May, so it's possible that the box-office performance of first "The Force Awakens" and now "Rogue One" has led Disney to stake out December for every "Star Wars" film.