Is the quarantine period in Thailand 14 or 15 nights for arrival before 6pm?

The discussion revolves around the quarantine duration for travelers arriving in Thailand under the COVID-19 regulations. While some report a standard quarantine period of 15 nights (16 days), others claim that arriving before 6pm could potentially reduce this to 14 nights. Several personal experiences vary, indicating that the count starts from the day of arrival, leading to confusion about the actual time required in quarantine.