From the EHAS website:
As of February 12 2021 the rt-PCR test time frame will be reduced from 120 to 72 hours, before departure to Sint Maarten for all travelers originating from a high risk country (last leg in case of connecting flights).

So a person flying from, say, Pittsburgh to Atlanta to SXM will need to have the test sample taken 72 hours or less before the day and time that the flight leaves ATL.