The characteristic frequencies in the plasma are much higher. Kilohertz and up. The steady state will be reached within seconds, so to the plasma 8 minutes is b

The characteristic frequencies in the plasma are much higher. Kilohertz and up. The steady state will be reached within seconds, so to the plasma 8 minutes is basically "infinity". But at that point the all the power that is leaking out of the plasma (50MW of heating times a Q of 10 implies that the plasma will output half a GW) will have heated the wall to the limit (and that is with active cooling of the walls). One could beef up the cooling to run at actual steady state (for an hour, or a day or a year), but it would not tell you much extra, so they didn't bother.