Just wondering if anybody has recent experience of this?

Rules say that you either need to be able to show a negative COVID-19 test within 72 hours of arrival or take a test at the airport in Madeira on arrival. Unclear to me when the 72 hours starts - time of sample or time of lab confirmation? I am thinking of taking the test on arrival - seems that results are available within 12 hours but does anyone have experience of this? What are you allowed to do in those 12 hours? Can we go to our hotel?