What is meant by the question, "Why are characters born at certain times and in certain places?"

One thing it can mean to say that "characters are born at certain times and in certain places" is authors create and use characters to fulfill their own purposes. They create and use characters to tell their own stories complete their own themes. Authors create themes to express their own opinions about the ways of the world.

While author Harper Lee protests that To Kill a Mockingbird is not autobiographical, it does indeed reflect her own life to an extent. To that end, author Lee created Scout and placed her in a certain setting in order to share with the world some of what she experienced and learned herself.

Like Scout, Lee was born in a small town of Alabama. A difference, however, is that Lee was born in Monroeville, whereas Scout was born in the fictional town of Maycomb. A second difference is that Lee is a few years older than Scout, having been born in 1926, whereas Scout's birth year can be traced back to 1929. Regardless of their three-year age difference, Lee, like Scout, grew up in segregated Alabama during the Great Depression. Also like Scout, Lee's father was a lawyer, who defended the accused before all-white juries in cases very similar to Atticus's. In addition, it is known that African-American Walter Lett was tried in Monroevill, year 1933, for a rape case with details nearly identical to the details of Tom Robinson's case. While Lee's father did not serve as defense lawyer, the Lees paid very close attention to the case, and Lett's story clearly served as some of the inspiration for Tom Robinson's story in To Kill a Mockingbird (Talmage Boston, "Who Was Atticus Finch?," State Bar of Texas).

Based on the few details we know of Harper Lee's life, we can see that Lee grew up being a witness to the injustices African Americans suffered due to racism, which clearly significantly impacted her. As a result, she developed a character very similar to herself who grew up in the same setting Lee herself grew up in order to develop themes concerning prejudices, racial tensions, and the need to "climb into [another person's] skin and walk around in it" (Ch. 3).