All six hours and twenty minutes.
The next step in the process is that the justices will meet in conference (by themselves, with no one else in the room) Friday morning. They will discuss and vote on the respective questions presented, in order of seniority. These votes are not binding; no votes are official until the decision is handed down publicly. But they give the Court a working count with which to assign and write opinions. (Votes do change after conference, but it is certainly the exception and not the rule.)
The audio and transcript should be up on the Court's site within the next hour. More coming soon.