This might be one of the most peculiar changes to history Tim makes, and it is only his third trip.
Mostly because he cannot work up the nerve, Tim never raises the "love thing" with Charlotte until it is almost too late. When he does, on her last night with them, she shuts him down cold, saying that it was a bad idea to wait until her last night. He takes her advice to heart, goes to his closet, and comes back one month sooner, when she has been there a month. This time she stalls him, suggesting that it would be better for him to ask her on her last night.
This he takes to mean that she has no intention of taking him seriously, and she is trying to put him off gently. He already knows what she says on her last night, and it did not work. But then, did he change history, or did he not change history?
In the original history, he never verbalized his interest in her until the last night she was there. Thus when he asks her on the last night, she brushes him off with the objection that he should have asked her sooner. It is, in that circumstance, a reasonable objection--he could have brought up the subject sooner, and he never did.
Now he asks her after the first month, and it is she who suggests that he ask her again on her last night. What is going to happen? He seems to think that what she did on her last night in the original history is what she will do this time, but this time is different. She cannot say that he should not have left it to the last night, because this time he did not do that, and she suggested that it would be a good idea.
Looked at from a different perspective, this time in mid July Tim asks Charlotte if she might be interested in him, and she says in effect that she might, she does not yet know, but they should talk about it again just before she leaves. That gives him hope, and a reason to talk to her again about it on her last night; it also means she really should expect that he will approach her again on that last night, and she cannot tell him that it was a bad idea to wait so long because this time it was her idea.
So perhaps in this history he does not ask her on the last night, because he already knows what she is going to say--but then, he doesn't know, no matter how we configure the matter. Assuming that the version of him that lives through that last month after that conversation is aware of the conversation, it will have given him hope and incentive to talk to her, because he does not know about the conversation still in his future. Assuming that this past version of him does not remember the conversation (because it was the future version who was in control of his body at that moment), he has no reason not to make the same move his other self did, and talk to her on her last night. Either way, he is going to have a different conversation with her, one coming from the history in which she, at least, remembers having told him to talk to her about it on her last night.
He might even get a different answer. That is, the answer has to be different, even if it is a different excuse, but she might decide to suggest they write to each other and see where it goes, or that she'd like to see him maybe next summer if nothing happens before then. She cannot say what she said the first time, and it is ridiculous for Tim to expect that she would, because he changed history and deprived her of that answer in the process.
So again the new trip gives us a new problem.