true. but on the other hand, the 'theoretical' is being turned into practice as evidenced by this 8 minute containment. the best a tokamak can do is half a second.
403s is about 7 minutes, so less than Wendelstein 7-X.
They could go longer. 7-8 mins is an arbitrary cut off out of fear that something might break (quench), knowing that enough data has been gathered for the time being.