According to a series of tweets from producer Michael Gamble, the DLC will likely be available after 7pm AEST for Xbox and PlayStation users, and as for we PC gamers? They plan to have the content available for download on Origin “before noon MST”, which is 4am AEST.
Also promised? A drop in the level of galactic readiness required to see all available scenes; a certain choice now requires ~3100 strength in assets rather than ~4000+.
And to see all the changes? Start from the assault on the Cerberus base (which, conveniently, is the autosave created for you after you finish the game).