The idea of being immune is utter idiocy and weird as well.
There is no immunity when the average flight time between the two nations is 4-6 minutes.
All the AAD offers is some protection for the eastern most cities.
There was a reason that despite various ABM measures such as the PATRIOT and otherwise.. the idea of IRBMs in any country makes people nervous. Smell the reality, you live under the very high potential of being BBQd to nothing.. regardless of how many PAADs you make.
Lets see.. anything dragging in other countries.. etc.
Why???
This is a terminal stage defence. How does it matter as to "how much time a missile that has to be intercepted has spent in transit" when the whole sequence of acquisition, targeting, and Interception takes place in terminal stage.