The 14-day self-monitoring/daily check-in requirement is listed as #14 on the Travel Requirements section of the StMaartenEHAS webpage at https://stmaartenehas.com/travel-requirements/

The only other mention that I've seen is in GaryB's report of the experience on his visit, which is posted at http://www.traveltalkonline.com/ubbthreads.php/topics/231638/3.html