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Done correctly you should receive your Thailand pass the same day, put plan for upto 7 days
Not sure what you mean by sandbox package, as the Phuket sandbox you have to book your SHA plus hotel separately to your pcr tests and transport from airport to hotel
seems there now allowing you to change to an earlier date, probably to give a chance to those who have a pass for after the 15th in case they do go ahead with that cut off date