*High time

It does not mean 'about time' -- it means the last appropriate time, verging on lateness.

One source's indication of its origin is Shakespeare's Comedy of Errors:

ANTIPHOLUS OF SYRACUSE:
There's none but witches do inhabit here;
And therefore 'tis high time that I were hence.

This is at least an early use. I suppose the meaning may be related to that for 'high tea'-- over to you, BrE speakers!