I don't mean to argue that it is clear that the duel lasted that long in MoR, but I doubt that Rowling would have that plot in mind. Also, from TVTropes:

It's strongly implied that Grindelwald was using the Holocaust to fuel some Dark ritual. Dumbledore mentioned that he was literally invincible while his Muggle allies were still making blood sacrifices for him, and they had to be stopped before he could be defeated. So yes, in those months where the wizarding world claimed Dumbledore was "waiting for the most dramatic moment," he was actually stopping the Holocaust.