I only remember it being a very late notification. May sounds about right.
As for my major, initially I was Astro. I switched to Math going into my junior year because I realized I did not want to be a developmental engineer for the AF but rather an analyst. There were a lot of factors which contributed to my decisions but the main points are that I wanted a foundational degree in something techy which the AF would want enough to all but guarantee that my AFSC will be analyst after graduation. Analysts often attend graduate school, which is another goal of mine, and make a comfortable living in the civilian sector after they separate.
I learned that I was not pilot qualified near the end of sophomore year.