The official Pokémon movie website has updated. Translations follow:

Media Information

Magazines:
Saturday May 11th: "Monthly Shonen Sunday" - Information on the pre-screening
Monday May 13th: "Betsucomi" - Information on the pre-screening
Wednesday May 15th: "Corocoro Comic" - Information on the movie

*Note that these are the scheduled publication dates, and as such are subject to change without notice.

Source: https://www.pokemon-movie.jp/news/?p=3634