The court gave no indication at the conclusion of the argument about when they would rule, but it was widely expected that the decision would come relatively quickly, since a stay is in effect and if the court finds a constitutional violation, then every day the stay continues works an irreparable injury - a deprivation of constitutional rights. Also, if, as seems possible, the court finds that the appellants lack Article III standing, it should promptly dismiss the appeal upon determining that it lacks jurisdiction over the case. Since the court agreed to "fast track" the case by holding oral argument just weeks after the appeal was filed and brief, it seems likely that the court would try to fast-track the decision as well.

But that doesn't necessarily mean speedy finality, because whichever side loses can petition for en banc review (by an expanded panel of the 9th Circuit, which is likely to be granted given the significance and notoriety of the case), and the ultimate losing party in the 9th Circuit could petition the U.S. Supreme Court to review the case. Even the Article III standing question by itself could be a relatively strong basis for Supreme Court review, since Justice Ginsburg's comments about proponents' lack of Article III standing in the Arizona case could be characterized as "dicta" rather than "holding" (i.e., not necessary for the Court's disposition of that case on the merits), leaving an arguably open important question for the Court to resolve on a recurring issue of federal jurisdictional law.