Butterfly season varies depending upon what part of the world is being talked of. For example, butterfly season in the New England region of the United States is in their summer during July to August (very short), while the butterfly season in South Africa is in their autumn and winter during March to July. In the Time of the Butterflies is set in the Dominican Republic, which, like other Temperate Zone locations, has butterflies all year round with the greatest abundance during their butterfly season from April to November.
Chapter 11 of the story covers the period of time spanning March, April, May, June, July to August. This is the early part of the Dominican butterfly season, the beginning of the time of butterflies. Chapter 12 covers the months spanning August, September, October to November. This is the latter part of the Dominican butterfly season, the ending of the time of butterflies.
In Chapter 11, between March and August, María Teresa faces horrific circumstances the worst of which is that which occurs in front of her husband. Witnessing María Teresa endure the horrific pain of electrical shock, he is coerced into cooperating with Trujillo. Nonetheless, the "butterflies" triumph when, in their time, María Teresa succeeds in secretly communicating her story of torture to an inspector of the Organization of American States.
In Chapter 12, between August and November, Minerva, after being imprisoned with María Teresa, reclaims her old courage and sense of purpose. Trujillo declares that of his two remaining obstacles to complete power, one is the Mirabal sisters. Undaunted by Trujillo's psychological attacks against them, like transferring Manolo and Leandro to distant and remote Puerto Plata prison, Minerva and the others make the dangerous trek there and arrive safely.
The Epilogue (epilogue: the concluding section that finalizes results of earlier events in a work of literature) covers the end of the month of November. Written by Dedé, it tells of the November deaths of the Mirabal sisters. On their return from Puerto Plata prison, they and Rufino are ambushed by soldiers and beaten. Their dead bodies are replaced in their car, and their car is pushed over a cliff-face to simulate the appearance of a car accident. The Mirabal sisters--the butterfly sisters--began to have their greatest victories when the butterflies in the Dominican Republic began to fly in freedom and liberty from their cocoons and met their deaths at violent hands when the butterflies in the Republic met their seasonal ends.
The underlying message suggested and symbolized by this parallel is that there may be a renewing season for liberty and freedom in the Dominican Republic even though this generation of butterfly sisters has fallen in death, along with the butterflies that symbolize their short, though triumphant and marvelous lives.
The Mirabel sisters are not known there, for which she is also sorry for it is a crime that they should be forgotten, these unsung heroines of the underground ....
March, and throughout early spring, in the Southern United States, is the time in nature when butterflies emerge from their cocoons. In Alvarez's novel, the Mirabel's reach their full maturity in March (Ch 11) and meet their early deaths in November on the 25th (Ch 12 and Epilogue).