Please note--they did not really answer your specific question. It is 120 hours for travel to SINT MAARTEN for a PCR test. The EHAS folks do not care (and possibly don't even KNOW) what the requirements are for French St. Martin. Please note they also do not even address the timing for an antigen test.

It is my understanding that, depending on where you're staying, you may be required to take another test on the French side, because their requirement is 72 hours . Best to ask this question of the folks where you are staying.