I would describe the tone as time-sensitive. I say this because the author keeps a date in the title and the sound of clocks marking the routines of a regular day:
Two o'clock, sang a voice.
Delicately sensing decay at last, the regiments of mice hummed out as softly as blown gray leaves in an electrical wind.
The voice in this piece certainly feels like a dystopian work. It feels void of humanity but full of the evidence of previous human existence. The references to technology make the piece feel mechanical or technological.
Ironically, the description of images feels positive, almost happy. It is as if sounds of life can be heard and the colors and textures of objects in the text are vividly imagined.
I would also describe it as empty. It is obvious to see how the humans have all gone. It feels like a society so mechanized that the mechanics have outlasted human beings:
The house was an altar with ten thousand attendants, big, small, servicing, attending, in choirs. But the gods had gone away, and the ritual of the religion continued senselessly, uselessly.
I would describe the tone of this story as lyrical or poetic. The "soft" in the title indicates this. The lyrical, gentle tone provides an ironic juxtaposition to a story of nuclear destruction.
An example of a lyrical passage is as follows:
The garden sprinklers whirled up in golden founts, filling the soft morning air with scatterings of brightness. The water pelted windowpanes, running down the charred west side where the house had been burned evenly free of its white paint. The entire west face of the house was black, save for five places. Here the silhouette in paint of a man mowing a lawn. Here, as in a photograph, a woman bent to pick flowers. Still farther over, their images burned on wood in one titanic instant, a small boy, hands flung into the air; higher up, the image of a thrown ball, and opposite him a girl, hands raised to catch a ball which never came down.
The five spots of paint—the man, the woman, the children, the ball—remained. The rest was a thin charcoaled layer.
The gentle sprinkler rain filled the garden with falling light.
The "golden founts" and "scatterings of brightness" as well as the gentle and artistic images, like photographs, of human beings doing ordinary things such as picking flowers or playing with a ball, make the reader feel acutely the senselessness and horror of nuclear war. Bradbury shows in images how the immense technology of war destroys ordinary people going about their everyday lives. By using lyrical images rather than telling us "war is bad," Bradbury allows us to experience the loss it brings emotionally.
Bradbury was a poetic writer who used imagery to make his point and no doubt was influenced by the language of the Teasdale poem he quotes. In his cautionary tale, he hopes the reader will understand how beautiful life is in all its ordinariness, even with the creepy undertone of the mechanical "mice" and "rats" that go about their business senselessly with no humans left to serve. Technology should not be allowed to be in control, the story says, for it is from human life that it derives its meaning: and without humans it quickly reverts to a state of nature, as the house does once the humans who lived in are dead.
The lyrical language mourns the loss of beautiful ordinary life that a nuclear war could bring--and, Bradbury hoped, prevent it.