I'm not sure if the "official" length has dropped yet, but the entire movie with credits is just over 4 hours long. I think somewhere around 4 hours and 5 mins. or something. The original plan was to split it into parts but HBO Max and Snyder ultimately decided to launch it as a movie with chapters that will aid in stopping/starting to make it easier for people. Debbie Snyder said HBO Max will have indications in the movie and the movie will also have its own indications on when a new chapter starts. There will also be a 10 minute intermission featuring music by Tom Holkenberg built in about half way to serve as a stop/start point and also aid in the future if there's ever a theatrical release.
Official premiere date is March 18th worldwide on anything HBO and in some countries VOD/digital purchase.