I don't know what action could be taken. The risk of mass anxiety and the behavior that comes with that is probably greater than any additional safety a vague 3 day warning would provide.
I would want to know, especially if it’s a large object and higher percentage probability, because then it’s a way to tell loved ones what we need to tell them and go forward together in love. We should always strive to do this, of course, but it would still be better to have the opportunity to do it.