当 … 的时候 (when …)

Freeze the moment it happened

• at or in the very same...当dāng … (of / 's)的detime时候shí hòu = "when / at the time when …".
• at or in the very same...当dāngI / me我wǒto return home回家huí jiā(of / 's)的detime时候shí hòu = "when I got home".
• at or in the very same...当dāng opens the time-clause; (of / 's)的detime时候shí hòu closes it.

at or in the very same...当dāng + Clause + (of / 's)的detime时候shí hòu，…

• at or in the very same...当dāng … (of / 's)的detime时候shí hòu frames the moment the main event happens.

when当dāngI我wǒget home回家huí jiāwhen的时候de shí hou，sky天tiāndark黑hēi了le。

• at or in the very same...当dāngI / me我wǒto return home回家huí jiā(of / 's)的detime时候shí hòu，to get dark天黑tiān hēi(completed / change)了le = "when I got home, it was dark."

Recap

Read the full reference: HSK 5 grammar — Nouns.