Music Practice - as a hobby or to make perfect performances?

That depends on what you want to achieve and also your level of talent. To understand the concept, not much time is needed. That is easily achieved during your class. To play for self-entertainment where perfection is not the criteria, a few hours of decent practice is enough for the average student. To make it a perfect performance, more time is definitely required. (Of course there are other things to overcome like musicality, stage fright, etc.)

For example: To understand the Shakespearean poetry, a few times of reading and some explanation in class are enough. To recite to yourself or family members where imperfection is tolerated, a few hours of practice are required. To recite it in public, you’d be inclined to practice everyday! In all the above, a highly talented person will get results faster than an average talent. Nevertheless, both will get there.

Here's some good advice: "John Erskine learned the most valuable lesson of his life, when he was only fourteen years old. His piano teacher asked him, "How many times a week do you practice, and how long do you practice each time?" He told her that he tried to practice once daily for an hour or more. "Don't do that," she responded. "When you grow up, time won't come in long stretches. Practice in minutes, whenever you can find them - five or ten before school, after lunch, between chores. Spread your practice throughout the day, and music will become a part of your life." Her advice obviously worked. Erskine became a concert pianist who performed with the New York Philharmonic, and he later served as President of the Juilliard School of Music and Director of the Metropolitan Opera Association. He also went on to teach literature at Columbia University and wrote more than forty-five books. His most famous work, "The Private Life of Helen of Troy", was written as he commuted to Columbia."