With Batman apparently on the fast track, the move ahead of Justice League 2 enables Zack Snyder to tackle his long-in-development thriller The Last Photograph.
Regarding the Ben Affleck Batman movie, Joe Manganiello seemed to indicate that it goes into pre-production this year, and both Manganiello and Jeremy Irons, who plays Alfred, stated filming on Batman starts next year.
The Batman movie has no release date; Ben Affleck is supposed to direct, and is starring in, and co-writing the script with Geoff Johns.
Justice League 2 had an initial release date of June 14, 2019; it's unknown if the Batman will take the release date or whether a new date will be announed.
