It is high time that( ).(你该写作业了)you did your homework.为什么是过去式?

It is high time that( ).(你该写作业了)you did your homework.为什么是过去式?
It is high time that( ).(你该写作业了)
you did your homework.
为什么是过去式?

It is high time that( ).(你该写作业了)you did your homework.为什么是过去式?
这是一个中学英语语法重点
It is （high/about） time 如果后面接从句 要接虚拟语气 动词要用过去时
又如 It is about time that we went home 是时候回家了

我们老师跟我们说是固定句式

这是虚拟语气。