Tail wagging the dog.
I know what the book says. The discussion is about whether the book is sensible.
If the roads don’t need to be closed when an aircraft is going to land with 31 minutes useable remaining on board, the roads don’t need to be closed if an aircraft is going to land with 29 minutes on board. That is, unless the 2 minutes difference increase the probabilities of an undershoot or overshoot.
And if some heavy metal is going to run out of fuel because it can’t land at e.g. Sydney in time, isn’t it going to force land/ditch somewhere other than close proximity to the airport, thus rendering road closures near the airport somewhat pointless?