Over how many years does Things Fall Apart take place?

Chinua Achebe’s Things Fall Apart is a post-colonial novel that takes place towards the end of the nineteenth century in a small, fictional Nigerian village. The setting is of utmost importance to the context of the text because Achebe explores the ways in which the European missionaries inflicted their political structures and institutions on the Igbo society. Therefore, the novel does not exist as a short, concentrated commentary, but rather as an ongoing observation of the behavior and interactions of both the Igbo and the European missionaries. 
The first reference to time in the novel occurs in Chapter One, when Okonkwo, the protagonist, beats Amalinze the Cat in a wrestling match. The text states, “As a young man of eighteen he had brought honor to his village by throwing Amalinze the Cat. Amalinze was the great wrestler who for seven years was unbeaten, from Umuofia to Mbaino” (1). The text then goes on to assert, “That was many years ago, twenty years or more, and during this time Okonkwo’s fame had grown like a bush fire in the harmattan” (1).
The next reference of time occurs when Okonkwo is given charge of Ikemefuna for three years after Okonkwo threatens a village to surrender a virgin and young man for atonement. The text states, “The elders of the clan had decided that Ikemefuna should be in Okonkwo’s care for a while. But no one thought it would be as long as three years” (20). The next major passage of time occurs when Okonkwo is exiled for seven years after he accidentally shoots and kills a boy at Ezedu’s funeral: “Your duty is to comfort your wives and children and take them back to you fatherland after seven years” (95). Okonkwo then returns to Umuofia, and upon seeing the influence that the European missionaries have exerted over his village, he commits suicide.
Thus, the book ranges over a span of thirty years.