I would think this.They didn't have exactly airtight building skills. So it'd be something from three days to a week probably.
In the real story the walls were covered in arsenic (?) also the executee has sensitive lungs so not long.
Air holes will extend the time to days instead of hours.A giant hampster bottle of water will extend the time to weeks instead of days.
Literally me when I was drafted to work on the Great Wall of China.
The state appreciates your sacrifice, comrade.