hahahahahaha. It is so simple yet so brilliant...i can't believe I have missed this technique.
I have never....never, never, never tried holding out a 2nd line G for 20 minutes.....WOW!
Along with all the other techniques I go through....more than 50 now....I will experiment with a whisper soft 20 minute G and see what happens.
I think the longest long tone i have ever held probably was in the neighborhood of 1 minute maybe and that was doing the Gordon Routine.