Crikey Hudson, are you sure that Boeing instructor was not pulling your leg?
!!! NEVER TOUCH THE BRAKES WITH YOUR HANDS !!!
I check my brake temps on a turnaround by touching the tyres with the back of my fingers. This will give an approximate indication of brake temp.
The back of the fingers trick I learnt from a fireman on one of my refresher courses, this is how they check the temp of a door or similar to judge how hot the fire is behind it. They use the back of the fingers because a) They are less sensitive so will be less painful if burnt and b) If an object is very hot the fingers will involentarily close around the hot object and you can't let go!
Back to your question. I cant quantify it but having touched my tyres on every turnaround I have ever done, I now know when they feel hot. If I find hot brakes (rare) I will get the F/O to touch the tyres as well to make the point about the relationship between braking techniques and brake temperatures.