The first couple 10-20 hours, it won't hurt, but you do feel slight pressure. NEXT DAY. HURTS. LIKE. AUFJBDFUBSJDFBDF. I still have my braces, one more year to go! After the 3rd day, you'll get use to it, and you wont really notice it anymore. The worst part of braces is just the 2nd day. Then they tighten your braces, it won't hurt as much.
ALSO. You will probably fast the 2nd day. (not eat at all, so make sure you make porridge!)