I'm so confused about time frame to test. I know it's 72 hours. Is that before arrival time in SXM or departure from USA?

Also when we arrive in February SXM and USA have a time difference due to Daylight Savings Time. Our arrival time is 12:05 pm so is it test by 11:30 our time or 12:05? And is it reasonable Ito expect to get results before my 7am flight? l'm losing sleep over this.