Can anyone explain the Summer Analyst Cycle timeline???

So generally the main pathway to break into IB is to get a SA internship during your Junior-Senior summer and then getting a return offer once you graduate if you do good. But how is the timeline for that big internship like? Cause it seems like the cycle for the junior internship opens at the beginning of your second semester of your sophomore year (January to February) and it means that you only have one summer and 3 semesters to somehow prove your salt to these banks, and majority of it you need to start preparing your freshman year and your freshman-sophomore summer. If you apply in the middle of your sophomore year for the super important Junior summer internship why do I hear about sophomore summer internships if you already applied to the Junior internship before sophomore summer?