We just returned less than a week ago and have gone through the process. Nowhere on our covid test did it give a time. Only a date. So there would be too way to count it in actual hours. We did our tests on Monday afternoon at 4:30 for a Friday departure. We wanted to make sure we had enough time for a Saturday departure in case we missed our connecting flight in Miami. Our results came in 24 hours but had the wrong date on them. It had Sunday's date instead of Monday and that would not have covered us through Saturday like we wanted. Since we got them late on Tuesday we had to wait until Wednesday morning to contact the clinic to get the date changed. That was done by noon on Wednesday and immediately uploaded to the site and within 1.5 hours we had approval. If you have a connecting flight, please read my earlier post entitled "AA Experience". Hope this experience helps others.