To say that Zack Snyder's Justice League is a bit of a mess would not be an understatement, nor is it a condemnation. We are talking about a movie that is four years old being put back together through the footage that was unfinished, footage that was complete, and footage that was recently shot. That's not easy to do, and it's going to be really interesting to see if we'll be able to tell the difference between the three different types of footage. Director Zack Snyder is active over on his Vero account (via ComicBook.com), where he has been revealing all sorts of details. That March release date sounds more and more likely, as Snyder recently said that we would be seeing new footage and anew poster soon.
Snyder has also been confirming all sorts of things on that Vero thread. While Zack Snyder's Justice League was called a "four-part miniseries" back at DC FanDome back in August, Snyder is now calling it a four-hour movie instead. The main difference between the two would be pacing since episodes of a miniseries, even one telling one story over the course of several hours, need some sort of beginning, middle, and end. This means that during the editing process, Snyder couldn't find breakpoints in the movie that would help split it up. That's a little worrying about the pacing, but any movie that is four hours long should come with a concern of pacing.
Finally, Snyder also confirmed that there isn't any sort of post-credits scene in Zack Snyder's Justice League either. It has been reported from Snyder and other sources that he is done with DC movies after this one and is ready to move on. Any sort of post-credits scene wouldn't make any sense if that was the case.
Zack Snyder's Justice League will be a four-hour movie that doesn't currently have an official release date, but Snyder did tell a fan that he would see them in March. Recently, a new fan movement sprung up asking Warner Bros. and HBO Max to #RestoreTheSnyderVerse, but this writer doesn't think that's a very good idea.