Question

it is the first time that是强调句吗

Answer 1

不是的，这只是一个固定句型
楼上强调句的判断方法没有说错
但这里去掉it is 和that以后句子语法并不成立
举例：It is the first time that I have read this book
去掉之后变成the first time I have read this book
但the first time不能作状语，这个句子语法是错的，可以作状语的是for the first time
也就是说It is for the first time that……可以作为强调句
但It is the first time that……只是固定句型

Answer 2

是的。
强调结构的特征就是去掉it is/was...that/who..原句不改变意思，还成立（符合语法等）

Answer 3

不是。
It is （was)the first time that...Have (had)done...
It was the first time that I saw her
若去掉，it was ,that
则为The first time I saw her
这是半句话，因为The first time 是引导时间状语从句的连词。
所以这并不是强调句。