I don't know, at least a month, a few months or even a semester. First of all, you should ask the music teacher in that school to be your tutor. He will teach you how to do it, and then prepare a lesson plan for class. The music teacher will help you. You don't have to worry. It seems that the school will send a list to the principal of the internship school after your internship. The headmaster will evaluate you. Don't worry, it will usually be well written. Then you return it to your school. In short, don't worry, just let you know something about teaching. That's how I got here. I wish you success!