If you've set up your AP scores to be sent to USNA when released, the academic advisors will receive and process them during plebe summer. For 2025, at some point during the summer (after English, chem, physics, calc 3 validation exams) every company had their turn for a 2-ish hour advisory session with no detailers (best day ever). They give you the list of classes you're signed up for in the fall along with all the courses you validated after taking AP scores and validation tests into account.
My advice - take all the validations you can. Everybody I know who validated a core class and chose to retake it regrets the decision (and often got worse grades). For chemistry in particular, if AP chemistry is fresh on your mind and you think there's a chance you could validate with some review, spending a few afternoons now brushing up will be so worth it to get out of chem 1 here (practice tests are available on USNA's website).
Also, even if you have no business validating a more advanced course (calc 3, physics, etc) just sign up for the test anyways had take the maximum time on the exam to take a nap, it's a nice break from the detailers. If you miss an exam you wanted to take talk to your academic advisor once the school year starts. My allergies landed me in COVID isolation during the physics 2 validation test, but I was able to validate the course by taking the physics 2 course final at the end of the semester after talking to my advisor.