Could you imagine a scenario where from warning to complete evacuation takes more than two days? Evacuating a whole area is a hard task, particularly once you start looking at more complex problems (elderly, prisons, hospitals).
I feel like the details of this are highly dependent on the confidence of the warning; moving large numbers of people (particularly elderly) will result in some deaths regardless. I guess more time to do it should help though.
We can't save everyone, so let's not bother trying to do better.