Well, there apparently is no discrepancy. First, the episode did not make it clear how much time elapsed between Jack and Locke’s chat in the hospital and Locke’s death. But in “There’s No Place Like Home”, Jack tells Ben that it’s been “about a month” since Locke visited him. And so the logical conclusion is that Locke’s mention of Christian, coupled with Jack’s semi-recent encounter with an apparition of Christian and breakup with Kate, gave a sufficient jolt to Jack to devote the next month to the idea of going back.
Where I would theorize a bit is that Jack was building up his courage (or trying to sufficiently swallow his pride) before re-establishing contact with Locke; it would be tough for a man like Jack to tell Locke he had changed his mind face-to-face. And that is why Locke’s death caused Jack to completely lose it--because he felt that his chance was gone, and it probably brought on another round of self-loathing. Poor Jack.
I would like to address one complaint about the most recent episode, which is that Locke was such a pathetic figure. I wouldn’t want it any other way. John Locke is a pathetic figure and has always been a pathetic figure. I think Jack gave the best diagnosis of Locke’s psyche in the last episode, although Sayid and Kate also made eloquent points. John Locke was pathetic when we first met him as a young man(chronologically)--stuffed in a locker, unable to recognize that he wasn’t a star quarterback/movie star/whatever the heck his delusional mind expected to be. He was pathetic when he was so desperate for a father figure that he did anything Anthony Cooper wanted--even after he had taken his kidney, he allowed him to ruin his one normal relationship. He was pathetic when he lived on a cultish pot farm. He was pathetic when he role-played that relationship as “just friends” on a phone sex line, and when he thought that telling his boss “Don’t tell me what I can’t do” as he walked out the door was some kind of great tell-off. He was pathetic when he crashed on the island and attacked those who wanted to get off. He was pathetic when he became a slave to the hatch and was blinded by Ben’s true nature as a prisoner. He was pathetic when he continued his rampage of destruction against any possible mean to leave the island, and when he knifed a woman in the back in cold blood. He was pathetic when he led half of his people on a suicide mission, and he was pathetic when he allowed Ben to manipulate him into letting Ben move the island. John Locke is a pathetic person.
Sure, we’ve seen some flashes of something better out of him, but he at his core a sucker who refuses to accept that he’s not some kind of superman, and that he’s just a regular guy. That’s not to say that he may not be capable of achieving great things, but he needs to attempt to do that as normal people do--through a successful career, a loving family, a passionate hobby, etc.
And certainly LOST is about character growth and development, and ideally we’d like to see our characters grow and evolve and improve, and many have throughout their time on the Island. But there was no way that Locke’s “bring everyone back to the island” campaign could possibly be the impetus for that growth.
Why do I say that? Because the whole nature of it was intertwined with Locke’s delusions--heroism, destiny, fate, what was supposed to happen, all of the claptrap that has led Locke astray almost all of his life.
I believe that the true character breakthrough for Locke would have to occur near the very end of the series. Imagine him sitting down for a chat with Jacob, and Jacob explaining how special he is and about how his whole life has been a runup to this particular moment when Locke can save the Island. And Locke looks him straight in the eyes, and calmly says “Screw you. I don’t need this silly island or you or anything to make my life meaningful. I am my own man and I will live on my own terms and you can fend for yourself.” Now THAT would be character growth.
The episode title does give me some inkling about what we’ll see, but if I’m wrong I’ll explain what I was expecting.