When do you get to download and try out the new! improved! endings to Mass Effect 3? It depends what platform you're on.
According to a series of tweets from producer Michael Gamble, the DLC will likely be available in the early morning (around 5:00 a.m. Eastern time) for Xbox users, sometime in the afternoon for PlayStation players, and as for we PC gamers? They plan to have the content available for download on Origin "before noon MST," which makes it 2:00 p.m. here on the East Coast.
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).