AP make up exam, how to proceed?

Hi,
My S21 is planning to take the AP Calc AB test on the make up day instead of the standard test day. He wants to do this because his class is now covering unit 8 and he wants more time to review units 1-7 before the AP test.
His AP guidance counselor told him to “just don’t open your test on the standard test day.”
I’m wondering if this sounds correct or if anyone has heard of a way to confirm in advance that he will be taking the exam on the makeup date rather than standard date?

I just don’t want to make a mistake by not notifying College Board in advance that he won’t be taking the test on the standard date.

Have you called CB? I would call them for sure.