Originally Posted by cherokeesam
As some of you have pointed out, that hint about "moral sacrifice" probably plays a huge role in Thor's choices. I suspect he becomes king almost immediately in the movie (unless Odin dies, in which case the story will likely take a different turn): he and Loki return to Asgard, Loki gets tried and convicted for his crimes, and Odin agrees that Thor has finally matured enough to assume the throne. And then later in the film, Thor will have to choose between ruling Asgard or staying on Earth, and I think it's pretty clear that he chooses the latter. (Confirmation that the movie begins and ends on Earth is proof enough of that.)
My guess would be that it is after the "huge hit"--the attack of the black ship, the scene with Algrim, possible death of Frigga, etc. Maybe Odin is weakened to the point that he feels compelled to name Thor king immediately.
It's stunning to think he would abdicate, though it addresses the practical issue of keeping him free to fight with the Avengers.