The issue with immediate border closings is they create a lot of confusion. What happens to planes in the air or taking off or who does the policy actually appl

The issue with immediate border closings is they create a lot of confusion. What happens to planes in the air or taking off or who does the policy actually apply to (see the initial iterations of the muslim ban where even the border agencies didn't have a consistent view of their own policy. The policy has to get out to the people at the border actually enforcing it too so it's either distributed early (meaning it will probably leak early and cause a rush then) or they only learn about it when everyone else does causing issues.