October is Bradbury’s favorite month; he has said as much, and it features in many of his books and stories. It is the central month of autumn, when things change most visibly: colors sweep the forests, and creatures age, alter, and die; and Halloween, with its thrills and chills, closes out the month.
One of Bradbury’s earliest story collections was titled The October Country (1955), although it included a number of stories from his very first book, Dark Carnival (1947). “The October Game” (1948) is a story about a man who hates October and plans to hurt his unloved wife during their 8-year-old daughter’s Halloween party. Another story is called “West of October.”
Halloween is Bradbury's favorite holiday, as well. His novel The Halloween Tree (1972), written out of Bradbury's disappointment that the Great Pumpkin never shows up in the 1968 animated Peanuts special, "The Great Pumpkin," has a history of the holiday and its significance related by Death himself.
So it should be no surprise that he would set a novel in the month of October, with two friends who were born a minute before and a minute after midnight on October 30-31.