Due to the secrecy of grand jury sessions, only the jurors, the prosecution, and the witness can be in the room. You can have an attorney present in the waiting area, and you are able to consult with that attorney after every question.
In theory, the questioning could go on forever, in that the prosecutor can ask a thousand questions, despite knowing the witness is going to take 5A. And, if the witnesse wants he (or she in this case) can stand up, walk out and discuss teh question with counsel, then come back and take 5A or answer.
It's only when immunity comes up that things get real interesting, because a grant of immunity in exchange for testimony takes 5A out of the picture, and a refusal to answer questions after a grant of immunity leads to contempt charges...