There should be a fan outside or in the attic that is attached to the Radon system piping. It must be running. There also should be a homeowner visable gauge to show if a differential is being kept on the slab. The system should be working before starting your test. I think 12 hrs but 24 hrs would be safer.
Radon systems generally operate 24/7. I have never seen one with a switch so that the system could be turned off. The only thing that could really be inspected is the U-tube type manometer or other vacuum gauge to assure that the system is operation properly. Also, looking at the electrical connections whether the fan is in the attic or at the exterior of the building is a good idea. EPA protocol also requires a label at every floor that the piping goes through identifying it as a radon system.