Question

It was at that time when I realized the significance of study这种用法对吗

我在语法书上看到it is...who...，it is...that这种表强调的语法。
我想表达的时候在那个时候我意识到了学习的重要，用it was at that time that I realized the significance of study，用两个that总感觉读不来不对。
不知道有没有it is ...when...表强调的用法？

Answer 1

It was at that time when I realized the significance of study这种用法对吗
It was at that time when I realized the significance of study
用强调句的时候，不能用when，只能是that。
即：it was at that time （that） I realized the significance of study。语法上是对的。

因that这个引导词引导从句时经常省略，这里与前一that确有重复的感觉，
可以：
1 省略从句引导词that：
it was at that time I realized the significance of study。表意并无差别。
2 把前边的that换成同义的词，如this，the之类，以错开单词的重复。
it was at this/the time that I realized the significance of study。

Answer 2

at 去掉 没有it is ...when... 表强调