The setting of the novel is of special significance. In reality, Pianosa is a tiny island in the Mediterranean, a few miles south of Elba, between mainland Italy and Corsica. In the novel, it is fictionally enlarged to include the location of Yossarian's 256th Squadron of the Army Air Forces in World War II. Setting the tone early, Heller has Yossarian refer to the squadron as the "two to the fighting eighth power." The squadron's assignment is to bomb enemy positions in Italy and eastern France. Yossarian is a bombardier in the squadron. He occasionally seeks escape from the madness and mortality of war by having himself admitted to the hospital, which, imperfect though it is, becomes a symbol of refuge. Although the hospital is a haven, it is reflective of the military with its emphasis on institutional routine and sometimes absurd formality.
Heller's use of time is also important and can be confusing. Most of the novel takes place in 1944, but flashbacks to 1942 and 1943 occur without warning. Briefly, Yossarian was in basic training at Lowery Field in Colorado in 1942. There, he first discovered the haven of an Army hospital. In 1943, Yossarian went through cadet training in Santa Ana, California. He arrives at Pianosa early in 1944. The novel ends in December of 1944. The French author Louis-Ferdinand Céline (1894–1961), especially through his novel Journey to the End of Night, greatly influenced Heller's approach to structure and time. After reading Céline, the author of Catch-22 chose to compose in a different realm of reality in which truth is more important than fact and essence more important than literal sequence. For the confused reader, a helpful guide to time in Catch-22 is the number of missions assigned by Colonel Cathcart or completed by Yossarian. The novel opens in the middle of the story (scholars use the Latin term in medias res, "in the midst of things"). It is August 1944, and Yossarian has completed forty-four missions. It is also at this time that he first meets the chaplain, which helps us date the scene. (Stephen W. Potts provides a thorough and well-documented chronology to the events of the novel in Catch-22: Antiheroic Antinovel.) Time is purposely out of joint in the book, and that is crucial because Heller's method of telling the story is episodic and relies heavily on his depiction of character.
