If you choose to move it to the make up day, be aware that in class practice/review is over after the regular date, so he will be on his own to stay fresh on the material for a week or two.

My test’s makeup date is nearly 2 weeks after the original, so I pushed kids to take it on the regular day even if they have another one the same day.

AP Physics 1 is notorious for being one of the AP tests that students do not do as well on.

https://apstudents.collegeboard.org/about-ap-scores/score-distributions

Even if it's only two subjects, not three subjects, I'd still vote for the make-up day for the non-physics exam if it's possible.