Hello dear teacher
Which one is correct
It was high time you did something.
It was high time you had done something.
Unfortunately, 'had done' is incorrect.
It was time he did something.
I have changed you to he, because to tell someone (you) that there was a past time for them to do something seems unlikely.
It's time you did something (now) is fine, as is:
The mewing of the cat was becoming more insistent. It was time he did something. He considered shooting the cat, but thought better of it. He slowly got out of bed and headed towards the kitchen ...
There is a phrase
It is time I did something.
So I can't use the phrase in the past as
It was (high) time I had done something.
If so, I am surprised.