I want to review this when you arrive tomorrow afternoon. It seems that the when-clause can modify either the infinitive phrase 'to review' or the verb 'want' in the main clause. - - Your question is not clear, but the 'when'-clause modifies the whole main clause, and that's what you should presume unless common sense tells you otherwise.
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Others were slain by those who had been their brothers-in-arms when they marched south with Mance Rayder, the King-Beyond-the-Wall.
Is the when-clause modifying 'had been' or 'were slain'? If it's the former, then the sentence imp