Do I need to be in a medium zone country 21 days before landing in Phuket for the Sandbox program?

The question inquires whether one must be physically present in a medium zone country for 21 days prior to applying for entry into the Phuket Sandbox program, or if the requirement is for 21 days before landing in Phuket. Commenters clarify that the requirement pertains to the duration prior to the departure flight to Phuket.