45 minutes and 00 seconds is very close (less than a quarter of a second difference) to :23:33. But there's no magical or particular reason why 45 minutes is an important time period to make a nice round number. :24 is a very convenient number (so many factors!) that's very close to the same time duration. That's 46.2963 minutes.

Or maybe you are referring to three quarters of the way through the major division. That's actually pretty natural too :75 like a percentage. Now dividing the major division into thirds is a little less convenient but I do that far less than I need to add and subtract times which this system makes much more convenient.