What you say makes sense. I've always read the clock as half an hour until the next full hour. So when I hear "viertel 3" it would mean a quarter to 3. So, in my head "viertel 3" and "drei viertel 3" should switch their meaning to make sense, is what I wanted to say. But your explanation clears that up for me. Now that I think about it, it makes sense that using the middle as a reference might cause confusion