Some Dates

Poul Anderson's After Doomsday was serialized in Galaxy, December 1961-February 1962, as The Day After Doomsday, then published as a book in 1962.

Its opening chapter is set forty-five to fifty years after the first atomic bomb, let's say in 1995 - still in the twentieth century. The Monwaingi discovered Earth twenty years previously, thus, in our arbitrary dating, in 1975. The U.S.S. Benjamin Franklin, with its paragravitic and superlight drives, has been out of the Solar System for three years, thus from 1992. Before that, Donnan, now in his mid-thirties, had been at sea and on the Moon while galactic civilization was spreading into this spiral arm. 

Thus, this is a novel of faster than light interstellar travel set in the twentieth century. Quite a thing.