Voici la page de l'immigration.
vous pouvez la trouver ici :
https://tratimmigration.com/thailand-visa-overstay-regulations/However, the Thai Immigration officials realise that sometimes people make mistakes and book a flight a day too late or their plans change, a flight is cancelled and they have to leave a day late. In cases such as these, with a few hours overstay, the 500 Baht overstay fine is usually waived.
If you are in a situation like this, don’t panic. Just explain to the immigration officer when you are being stamped out of the county. Apologise and you will be treated fairly.
Children under the age of 15 are not charged a fine for overstaying but still get overstay stamps when they leave the country.
C'est bien l'heure de départ du vol qui compte et pas l'heure de passage à l'immigration. Le non payement de la l'amende dans ce cas est donc une tolérance et pas une obligation.