The official Pokémon movie website has updated. Translations follow:

Media Information

Magazines:
Monday May 14th: "Weekly Post" - Pre-screening announcement
Tuesday May 15th: "Corocoro Comic" - Presentation of the new Pokémon and pre-screening announcement
Wednesday May 16th: "DIME" - Pre-screening announcement

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

Source: http://www.pokemon-movie.jp/news/?p=3306