The danger zone is for about a minute or less in pregen, just a DIC indicator saying not to turn car off and keep driving and the car to be smart enough to not let you turn car off would work fine. It would almost rarely ever happen. The whole problem would be solved. Or three colors on the light, red for don't turn off, yellow for regen, green for finished.The problem is, during the pre-regen danger zone, the regen indicator is still off. You have to look at other parameters (manifold pressure) to determine when you are in the danger zone.
From my experience, it's roughly 10-15 minutes in the CTD, give or take.