If you have an I-20 from a college, you've already been officially accepted to that college and your SEVIS records updated, and you will start school when the semester starts, so 60 days doesnt apply here. 60 day rule applies in cases when your OPT has expired and you havent yet enrolled at a college and obtained an I-20.

However, if you're waiting to hear from another school where you have or plan to apply, and if they accept you, you very well 'might' have to go through the process of getting SEVIS release from the school that has currently issued you the I-20 and then only be able to get a new I-20 from the second school - please consult with the second school as to what their policy or process is regarding situations like yours.

Good Luck.