My daughter is at IU Bloomington studying Music Performance (oboe), and it is tough to do almost anything else when you are majoring in Music Performance.
She is expected to be doing 3 hours of practice per day, and that is the minimum. This is done outside your regular class time. Then there are the rehearsals for the orchestra/band you are playing with, additional rehearsals for ensembles, time needed for reed making, the Master Classes (which are also at night). Then, you get to do your regular classes. I never realized how much time and effort goes into training as a classical musician; but, it is your life with little time left for anything else.
She had thought about a double major, but nixed that idea when she learned about all the other time-consuming activities were involved in this course of study. She is getting a French minor. Something that helped a lot, though, was taking AP and college credit courses in H.S.
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.