动词 + 了 + 时段【dòngcí + le + shíduàn】

A length of time after the verb says how long something went on. The basics – verb copying with an object, 的, and the second 了 for "still going" – are in the duration point. Two cases work differently: a pronoun as the object, and a verb that happens in an instant.

A pronoun goes before the duration

When the object is a person – 我, 他, 你们 – it goes straight after the verb and 了, and the duration follows it.

• × 我等了一个小时他 → 我等了他一个小时

An object that is a thing still goes after the duration: 我看了一个小时书.

Time since a one-off event

来, 到, 毕业, 结婚, 离开 and 认识 happen at a point; they can't last an hour. A duration after them counts the time since it happened. The object comes before the duration, and a 了 at the end says the count runs up to now.

• × 我认识了他十年 → 我认识他十年了
• × 他来了中国三年 → 他来中国三年了

Asking

多长时间 and 多久 go in the slot where the duration would be.