The time that goes into music training is truly astonishing, you're right. And, three hours a day of practice really is a minimum! Harvey Phillips and Bill Bell required a commitment of four hours a day, excluding lessons, rehearsals, master classes and performances.
My daughter is currently in the Prep Division at Manhattan School of Music, in the top orchestra. The level of performance is very impressive: at least as good as a mid-ranking professional orchestra. I was blown away at their performance of Berlioz' Symphonie Fantastique a couple of weeks ago. I am amazed at these kids' dedication.
Yes, she was telling me about a senior who is about to graduate and that she is practicing 8 (!) hours per day. She is working her way up to more practice time.
As for the 5-6 years to graduate with a Bachelor's degree; due to the AP and college credit courses she took in high school, my daughter is technically finishing her sophmore year, but is rated a Junior. She figures to have enough credits to graduate after the first semester of her senior year. She is thinking of using her time after that preparing for auditions for graduate school.