as for the professionals in classical ensembles - they do practice for about 6-8 hours a day, but thats not because their routine is so inefficient - its simply because most of those pieces are extremely long and extremely difficult to master. so they lock themselves like 3 - 5 months in a padded room before they go out and perform the pieces. then, after having performed a certain programm for like half a year live, they lock themselves again in that room with the next set of pieces.