The ISB routine is rigorous, with a heavy workload and limited time to complete it. You will have class quizzes every week and exams every fortnight, in addition to other extracurricular activities and assignments. However, once you become accustomed to it, you may find that you enjoy the challenge. 

It is important to have decent academic skills, as evidenced by a GMAT score in the range of 600 to 770, but it is also important to note that your performance in class quizzes, assignments, and other activities also plays a role in determining your grade. If you are considering applying to ISB, it is important to focus on your application and not let the rigorous routine discourage you.