Question

修饰time的定语从句用when 还是that

Answer 1

都有可能。
区别的关键在于time放入定语从句中，是做句子的时间状语还是主语/宾语等名词性成分。

1. 如果定语从句缺少时间状语，一般用when
如：There was a time when the song was popular.
a time在从句中做时间状语
2. 如果定语从句缺少主语/宾语等名词性成分，则一般用which/that，有时还可以省略。
如：I‘ll never forget the time (which/that) I spent with you.
the time在从句中充当spent的宾语

另：下列句型中固定用that
This/It + is/was + the first/second... time +that从句
It be (high/about) time that从句

Answer 2

都有
He came at a time when we needed help .
他在我们需要帮助的时候来了。
This is the first time that I have visited the city (前有序数词时一般用that)
这是我第一次参观这个城市

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Answer 3

要看在哪里用了，如果It is time 就可以用that

Answer 4

时间状语用when,time当几次讲，用that