当 … 的时候 (when …)

A phone call during cooking is not a call after dinner

• Original account: when当dāngI我wǒcook做饭zuò fàn(modifier / structural particle)的detime时候shí hòu，phone电话diàn huàring响xiǎng(change or completed event, in context)了le。 places the ringing phone within the time when I was cooking. It does not say that cooking had finished before the phone rang.
• I我wǒto make做zuò完饭wán fànafter以后yǐ hòu，phone电话diàn huàring响xiǎng(change or completed event, in context)了le。 instead places the call after I finished cooking. The phone is the same, but the time relation has changed; grammar cannot rescue the dinner from an interruption.

Frame a time with when当dāng … (modifier / structural particle)的detime时候shí hòu

• when当dāng + clause + (modifier / structural particle)的detime时候shí hòu，main clause provides a when/while frame. In when当dāngI我wǒget home回家huí jiā(modifier / structural particle)的detime时候shí hòu，to get dark天黑tiān hēi(change or completed event, in context)了le。, the homecoming is the time frame for the statement about darkness.
• This taught full pattern ends its time clause with (modifier / structural particle)的detime时候shí hòu. Chinese also has shorter time expressions such as I我wǒget home回家huí jiā(modifier / structural particle)的detime时候shí hòu and at once当时dāng shí; this is not a rule that every use of when当dāng must contain the same closing words.

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

Let the actions determine moment or interval

• In when当dāngI我wǒcook做饭zuò fàn(modifier / structural particle)的detime时候shí hòu，phone电话diàn huàring响xiǎng(change or completed event, in context)了le, cooking supplies an interval and ringing happens within that frame. when当dāngI我wǒto / arrive到dàohome家jiā(modifier / structural particle)的detime时候shí hòu can frame the point of arrival instead.
• when当dāng…(modifier / structural particle)的detime时候shí hòu does not impose one fixed action duration. Read whether the event is a process, an arrival or a repeated situation; do not translate every example as either “after” or a long continuous action.

while当dāngI我wǒcook做饭zuò fànwhen的时候de shí hou，phone电话diàn huàring响xiǎng了le。

A time frame does not establish a cause

• when当dāngI我wǒto / arrive到dàohome家jiā(modifier / structural particle)的detime时候shí hòu，to rain下雨xià yǔ(change or completed event, in context)了le。 puts rain and arrival in a time relationship. It does not prove that my arrival caused the rain.
• Likewise, the phone ringing during cooking does not say who called or why. Timing, cause and identity are separate claims; additional words are needed to establish the latter two.

Keep the relationship in a new scene

• You were reading when a friend arrived: when当dāngI我wǒto read看书kàn shū(modifier / structural particle)的detime时候shí hòu，friend朋友péng yǒuto come来lái(change or completed event, in context)了le。 fits that frame. If the friend came only after you finished the book, use a completion-plus-after expression instead.
• For a future or recurring situation, the surrounding sentence supplies its time: when当dāngyou你nǐto need需要xū yàoassistance帮助bāng zhù(modifier / structural particle)的detime时候shí hòu，to / for / give给gěiI我wǒto make a telephone call打电话dǎ diàn huà。 — Call me when you need help. when当dāng…(modifier / structural particle)的detime时候shí hòu alone is not a past-tense marker.

Ask when, then check what remains unknown

• Identify the time-frame clause and the main event. Choose when/while versus after from their stated relationship, without inventing causation or an exact duration.
• The cooking, rain and reading scenes are original examples. Compare the full unit reference and the since (a previous event)以来yǐ lái lesson: a during-event frame and a since-period do different jobs.