I believe it is a good case for the Court to pick up, at any time.
Although, I do not understand why the District chose to Appeal the case to begin with, as the D.C. Circuit ruling was sound, in my own opinion, but, more importantly, I also believe the District Government has no legal standing to exist at all, as the Constitution places sole control of the District of Columbia in the hands of the United States Congress.
I see the Right to Keep and Bear as carved in stone, and not a Militia only Right as the Militia is covered in other sections of the Constitution, the Founders, in my opinion, not needing to expressly state that the Militia only can keep and use Weapons in the Second Amendment.
I believe it is high time for the USSC to put the States (and in this case the District) in their place and force them to extend a Constitutionally protected right to all Citizens.