Golly! Is that the time?
Gosh, is that the time?
Good Lord! Is that the time?
From dictionaries: "used to express surprise, shock or worry".
What does Is that the time? mean ? In which case one says this phrase? To express surprise at the fact that "it is high time" ?
No, you need to think of them in completely separate contexts.
"Is that the time?" -- This simply means it is later than you thought it was. Perhaps you thought was had been chatting for half an hour and realize that an hour has passed. Perhaps you went on a picnic and then realize you stayed so long you were going to get caught in rush-hour traffic getting home. It simply means it is later than you thought.
"It's high time..." is used to mean that you think something should have happened before now.
It's high time we left. (We probably should have left earlier.)
It's high time you got a haircut. (Your hair is already too long.)
The have little in common.
I too am more used to seeing it with a past tense verb.