Pattern
Time when before the verb; duration after the verb or object pattern
Core idea
Mandarin treats the time when something happens differently from how long it lasts. A time-when phrase sets the event in time and usually comes before the verb phrase. A duration phrase measures the action and usually comes after the verb pattern.
This distinction prevents a lot of English-shaped word order.
Mini decision rule
Ask two questions. “When did it happen?” gives a time-when phrase. “For how long?” gives a duration.
Keep time-when phrases near the front of the event. Put durations where they can measure the verb.
Examples
我昨天看书。
Wǒ zuótiān kàn shū.
I read yesterday.
The time tells when the event happened.
我看书看了一个小时。
Wǒ kàn shū kàn le yí ge xiǎoshí.
I read for one hour.
The duration tells how long the action lasted.
她明天工作两个小时。
Tā míngtiān gōngzuò liǎng ge xiǎoshí.
She will work for two hours tomorrow.
Common mistakes
Avoid
我看书昨天。
Use
我昨天看书。
A time-when phrase normally comes before the verb phrase, not after the whole event.