I would interpret it to mean 45-60 minutes after reaching 102°. I have found that part of what makes this an art, rather than a science, is getting all the variables to meet at the right point - pH, dryness of curd, heat, and then later pressing or cheddaring time vs. pH.
One thing I want to look into more is the issue of buffering - some things in milk will buffer the pH, slowing down its progression. But I need to go back and read more - I recall seeing this, but at the time it kinda went in one ear and out the other.