What is the general temporal and geographical setting of "I Have No Mouth, and I Must Scream"?

In "I Have No Mouth and I Must Scream," Harlan Ellison sketches a grim and disturbing nightmare of a future by which the last survivors of humanity are being ceaselessly tormented and tortured by the sadistic machine intelligence AM. This is a story set in a post-apocalyptic world. All of humanity has been rendered extinct, save for the story's protagonists, whom AM has preserved so it can continue to have victims to torment. Their torture is motivated by AM's sadism and by its inconceivably deep hatred of humanity.
In terms of physical geography, the story is set entirely underground, within the vast series of complexes which houses AM. It is a world where conventional geography doesn't mean anything anymore, given that humanity has been destroyed and its survivors are under the domination of the machine intelligence.