I read this quote from the CDC reported by jcaron:
If I have one or more connecting flights to the US, does the 3-day period apply to the first flight or the last one? Do I need to get another test if I have a connecting flight?
If your itinerary has you arriving to the US via one or more connecting flights, your test can be taken within the 3 days before the departure of the first flight.
If the 3-day testing period expires before one of your connecting flights, you only need to get retested before boarding connecting flights if:
- You planned an itinerary incorporating one or more overnight stays en route to the US. (NOTE: You do not need to be retested if the itinerary requires an overnight connection because of limitations in flight availability.), OR
- The connecting flight is delayed past the 3-day limit of testing due to a situation outside of your control (e.g., delays because of severe weather or aircraft mechanical problem), and that delay is more than 48 hours past the 3-day limit for testing.
How does the CDC define an overnight stay?
E.g. any stay longer than x hours and including midnight? If the stay is between x AM and y AM, which set of {(x, y), x<y} turns it into an overnight stay? etc.
I don't mean to be overly scrupulous but a friend of mine is flying to see me in the US and his flight has a layover between 5 and 8 hours from very early AM (quite close to midnight) to the beginning of the morning, and I genuinely have no clue whether the CDC defines it as an overnight stay.