AP and SAT preparation share content in one direction and compete for time in another.
Where they help each other
AP Calculus and AP Statistics feed SAT mathematics directly. A student working at that level finds the SAT mathematics section comfortable and needs only format practice.
That is the whole of the overlap on the academic side.
Where they do not
The SAT reading and writing section gains nothing automatically from a science or mathematics AP. It has to be planned as its own piece of work.
Students carrying several quantitative APs often assume the verbal section will follow along. It does not, and that assumption costs a second sitting.
The calendar collision
AP exams fall in a fixed May window. SAT sittings are held on set dates through the year, and one of them lands close to that window.
Taking the SAT during AP season means preparing for both in the same fortnight, at the point where the AP load is at its peak and cannot be moved. Choosing a different sitting removes the problem entirely.
Sensible sequencing
Take the SAT well before or well after the May window. Autumn and late summer sittings both work.
For a student taking APs in two consecutive years, the gap after the first May is usually the cleanest window available.
Practical step
Write the AP exam dates and the SAT dates on one page at the start of the year, then choose the SAT date from what is left. That one page prevents nearly every problem in this pairing.