Right after the death of Smaug is my guess.
That's my guess too, but that sure doesn't leave much for a third film. The breaking point for the first flim was the obvious breaking point IMO. But there is no good breaking point after that, which is probably why two films was the plan all along. I think the very late game change will probably end up hurting the series in the long run rather than do it good.
They're going to have to add a heck of a lot of stuff in the third film to fill it out. Because otherwise its 1 Big battle, exchanging of gifts, more Hobbit hugging, and then going home. And logically the Necromancer stuff will be in the second film. I can't imagine them leaving Gandalf out of 80% of the next film only to have 80% of the third film telling us where he was in the second film.
The whole Azog thing will pay off in the third film's battle, but I don't see why he needed to be included in the first film like he was. Bolg could have been that part and saving the return of Azog for the big surprise of the third film.