If one takes the flight XXX ->YYY->ZZZ, with a layover at YYY where one left the airport, does airport XXX or YYY count as the 1st embarkation point?

https://www.iatatravelcentre.com/world.php -> United States indicates:

Passengers entering or transiting through the USA must have a negative COVID-19 test taken at most 3 days before departure from the first embarkation point. Tests accepted are: antigen, NAAT, RT-LAMP, RT-PCR or TMA. Passengers details (e.g., name and date of birth) in the certificate must match those stated in the passport or other travel document; and the test result must specify "negative" or "not detected". If marked "invalid" it is not accepted.

If one takes the flight: airport XXX (not in the US) -> airport YYY (not in the US) -> airport ZZZ (in the US), with a layover at YYY during which one left the airport and reentered it, does airport XXX or airport YYY count as the first embarkation point? The purpose of defining the first embarkation point is satisfying the covid-19 requirements.

Assume that:

airport XXX and airport YYY are in 2 different countries,
the layover at airport YYY lasts less than 24 hours,
the flight XXX ->YYY->ZZZ is on a single ticket,
no checked baggage will be retrieved and re-checked at airport YYY: all baggage are checked at airport XXX through to the final destination (airport ZZZ),

in case this changes the answer.

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Can you leave the airport during a 3 hour layover?

Yes, you can leave the airport during domestic layovers. For instance, if you're a US citizen and have a layover within the country, it is legal and safe to leave the airport. Be aware that you'll probably be getting two boarding passes if the domestic layover is more than an hour.

Do I have to recheck my luggage on a layover?

When you purchase a layover flight, you will need to claim your bags when you land at your layover destination, and recheck them the next day when you continue your flight(s).

Is 2 hours enough between connecting international flights?

Consider allowing at least 60 to 90 minutes for a U.S. domestic connection, and at least two hours for an international connection. Airlines usually allow you four hours or more maximum connecting time.

Do you use the same ticket for a layover?

It gets a bit more complicated if your flights are with two different airlines. You might only receive your first boarding pass when you check-in for the first time. If so, then you will have to find the correct ticket counter at the layover airport and get your second boarding pass for the new flight.

FIRST INTERNATIONAL FLIGHT? : Travel Tip, Airport Walk, Flight Preparation | Jen Barangan

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