Braces Elastics/Rubber bands?

I have had my braces since the beginning of december 2008, and got my rubberbands at the beginning of april this year. I already feel that the bite is the exact same on both sides, and they were fixing a cross bite. Since april i've been wearing the "kangaroo" ormco zpak elastics, and was wondering if anybody could tell me the estimated time i have left. i wear them 24/7 and have doubled up a couple times. when i take them off they don't seem to move back. i'm going to the ortho tuesday, but i would like to be prepared on how much longer i have. thank you(: