When first paring your Wave Mini with your tablet or phone you will see your first measurements appear within 5 minutes. While the temperature and humidity are ready to go, the VOC sensor will need some time to calibrate. You can see this from the Airthings App (highlighted in yellow below).
Why do I need 7 days to calibrate the VOC sensor?
Wave Mini will calibrate itself over these 7 days to get rid of any VOCs that are remaining inside the device as a result of its production and adjust the new environment.