What is the validity of the Antigen Rapid Test (ART) certificate? Can you explain the 24 hour period?

The typical validity period of the Antigen Rapid Test (ART) certificate is 24 hours. Please note however that the 24 hours should cover the entire duration of the event (e.g. if the event is from 9am to 5pm tomorrow, the ART test should be taken only after 5pm today).