Screening and timing information has yet to be revealed, but we should find out more later this month at AnimeJapan 2018. The event takes place at Tokyo Big Sight from Thursday, March 22 to Sunday, March 25, and a Re:ZERO cast stage event is planned for Kadokawa's booth on the final day.
In addition to limited goods—including an A3 tapestry of the new visual below—voice cast members Yusuke Kobayashi (Subaru) and Rie Takahashi (Emilia) will appear as guests. Look forward to the latest information on the new content and theatrical OVA screenings at the event!
The September announcement video:
Via Comic Natalie