时间状语从句是在复合句中，由特定的连词引导，用来表示时间关系说明主句动作发生时间的从句。
二、引导时间状语从句连接词
before, after, until/till, as soon as, when, while, as, since，the minute, the moment, each( every, next, the first) time等
三、时态
时间状语从句中一般用一般现在时或一般过去时。
其中when、not..until....、as soon as要遵守“主将从现”原则。
四、具体分析
1. 辨析：when, while, as “当…时候”
★ 结构：
过去进行时(主句) +when+ 一般过去时(从句)
过去进行时（主句）+while+过去进行时（从句）
when既可以指"时间点",与瞬间动词连用，也可以指"时间段"，与延续性动词连用（=while）。
while表示时间段,因此，while引导的时间状语从句的谓语动词要用延续性动词。
while 表对比“然而”时，前后动词时态一致！
as time goes by/on随着时间的过去
2. since
重要句式：It is +一段时间+ since+ 从句 (一般过去时)
例句：
It is four years since my sister lived in Beijing.
3. until, not…until表示“直到```才”,在肯定句中主句常用延续性动词；在否定句中主句常用短暂性动词。
肯定句：I waited until midnight.
否定句：I did not leave until midnight.
注意点：
1）not until…在句首，主句用倒装
eg: Not until you had explained how did I manage to do it.
2) It is not until…that…引导的强调句
It was not until it was dark that he came back.
4. the minute, the moment, each ( every, next, the first) time作连词不和when 连用
5. Hardly/scarcely…when, no sooner…than, as soon as表示为“一```就```”
例句：
I had hardly/scarcely got home when it began to rain.
I had no sooner got home than it began to rain.
It began to rain as soon as I got home.
注意点：Hardly/scarcely…when, no sooner…than位于句首，主句用倒装
例句 :
Had I hardly/scarcely got home when it began to rain.
No sooner had I got home than it began to rain.
