The place is the south.
The time probably the late 19th century based on the fact that the author has stated that:
"Much of Becky McKelva's background is drawn from her mother's life in West Virginia. In fact, the novel was written not long after her mother's death, a period in which Welty was recalling her mother's life and experiences."
Eudora Welty was born in 1909, so her mother's life would have been during the late 19th century, which places this story in the 1880-1890s.
The major event is the death of Laurel's father. After her father's death, Laurel goes through a series of grief related experiences where she explores her family's history.
The main theme in this book is making peace with the past and family relationships.
"In The Optimist's Daughter Laurel is forced to make peace with her past and her present in order to go on with her future. The event of her father's death is difficult for her because she enjoyed a loving relationship with him, and even more so because his recent marriage to an angry selfish woman."
"In the end, Laurel is only able to leave her hometown and her childhood home behind because she has examined honest memories of her parents and made peace with the decisions they made and the people they truly were."
I am not so sure I agree with the time frame in the answer given since the 19th century would mena the 1800's. The reason for this is that Laurel's husband was killed in WWII which took place in the 1940's and since the story takes place several years after his death I would have to say that the time frame is between the 1950's and 1960's.