New rules requiring international air travelers arriving in the United States to obtain a negative COVID-19 test within one day of travel will take effect Monday at 12:01 a.m. ET (0501 GMT), according to an order issued late Thursday.

https://www.reuters.com/business/healthcare-pharmaceuticals/new-us-covid-19-international-travel-testing-rules-take-effect-monday-2021-12-02/