“how long”通常用于询问持续时间，常与完成时态搭配使用。以下是常见时态及用法总结：
| 时态 | 结构 | 例句 |
| 现在完成时 | have/has + 过去分词 | I have lived here for five years. |
| 过去完成时 | had + 过去分词 | She had worked there for two years. |
| 将来完成时 | will have + 过去分词 | By next year, he will have finished. |
“how long”也可用于一般现在时或一般过去时，但较少见。例如：“How long does the meeting last?”（现在时）或“How long did you wait?”（过去时）。
