In simplistic terms - think three legged stool - athletic/fitness, academic, extra-curricular. Be good in all three, be great in one. You pick your one area of greatness, but I have never seen a successful candidate who was only good in each and not great in one. I simplify the personas to athlete, mathlete, and band kid. The SA pick from all three to create a well rounded student body.
From a standardized test perspective, as a HS Junior right now, your DS should be laser focused if this is the highlighted area of weakness in his portal. Different schools handle this type of thing differently, but I can't see them not letting your progress at your own pace up until the official deadline for applications. Once that window closes, I would expect them to start issuing TWE to those who really are not prepared.
The best part is that you have time! Congrats! Let's hope your DS makes the most of it. You never know if he will only have 1 shot at the exam under the current circumstances.