When to test for US

So the US rule says you need to test 1 calendar day before travel. We are on a 4:15 Alaska Airlines flight to LA. Does anyone know what “1 calendar day before” means? Does it have to be less than 24 hours before we leave, meaning taken after 4:15 the day before, or does it mean any time the day before?

The testing at our hotel stops at 5 pm and there’s always a line, so that would give us a pretty narrow window for testing. I don’t want to test too early and get turned away at the airport.