Most people have no idea how large the number "million" is in the context of human beings. Evacuating a couple of million people from a major metropolitan area is no easy feat -- and is damn near impossible without starting weeks in advance.
Actually, all the plans that have been worked up say it can be done in 72 hours.
That is, of course, if you IMPLEMENT the plan.
As far as I can see, the NO plan was "It Will Turn."