第二年第一百八十三天

[nnozomi]

语法
当 + X + 的时候, "when X..."
https://resources.allsetlearning.com/chinese/grammar/Expressing_%22when%22_using_%22dang%22

词汇
刻, a quarter of an hour (pinyin in tags)
https://mandarinbean.com/new-hsk-2-word-list/

Guardian:
当光线垂直射入镜面的时候, when light rays strike the mirror surface vertically
当你看到这封信的时候, when you saw this letter
[no 刻 of this kind]

Me:
当你去中国的时候，小心空气污染。
就算只是一刻，我也等不及了。

Comments

[grayswandir]

当光线垂直射入镜面的时候, when light rays strike the mirror surface vertically

I just looked this up out of curiosity, and I think 垂直 may mean "perpendicularly" here, since if I remember, the angle of the light in this episode is actually horizontal, hitting the mirror that's standing upright. (It's a new word to me either way!)