punctuation rules change?

should there be a comma or a semicolon in the blank on this sentence?

After reading “Heart of Darkness,” who could ever forget Kurtz’s dying words__”The horror. The horror.”?

I think it should be a comma, because it's not a title quotation, it's somebodny stating something. and how about these two sentences, which punctuation is correct?

Jack worked overtime to pay off his debts; at least, that was his explanation for his long hours.
Jack worked overtime to pay off his debts: at least that was his explanation for his long hours.
Jack worked overtime to pay off his debts, at least that was his explanation for his long hours.
Jack worked overtime to pay off his debts at least; that was his explanation for his long hours.

I believe it is the third one. I used Turabian 3.79 to come up with that answer.
What do you think?

[Casiopea]

1- After reading “Heart of Darkness,” who could ever forget Kurtz’s dying words, "The horror. The horror."

2- Jack worked overtime to pay off his debts, or at least that was his explanation for his long hours.

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