It's always been 3 full days. I promise you there is not a guy sitting there with a stop watching clicking down to 5pm or whatever is 72 hours from the minute you were swabbed thousands of miles away.
Anyone else find it bizarre how they still can't seem to figure out if the rule is 72 hours or 3 days (which gives more flexibility) after all of this time. Or did it change again? And yes, if you have a 4pm flight and a test with a time on it there is a huge difference