核心问题
（1）I recognized him at the first moment I saw him.
(2) We liked each other from the first instant we met.
(3) It was full dawn by the time he reached the road.
斜体部分与前面的名词是什么关系？如果是定语从句，那么其间省略了什么词语？
词典解答
可以认为在名词中心词与定语从句之间省略了关系副词 that 或 when。实际上，也可以不省略这个 that 或 when：
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At the first time that I saw him, I recognized him. 第一次看到他，我就认出了他。
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I sent you the news from the first instant that I heard it. 我一听到这个消息, 就把它寄给了你。
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At the first moment that he had said it he knew what mistake he had made. 他刚一说出了这件事，就知道他犯了一个什么样的错误。
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There have been moments in history when remarkable progress was made in relatively short periods of time. 历史上有过这样的时候:在相当短的时期内取得了惊人的进步。