The events depicted in The Godfather start in 1946 as we are told early in the movie as Michael has just returned from fighting in the war.
But key later events take significant time. Michael spends enough time in Sicily to get married and witness his wife die. When he returns to the USA he waits at least a year before contacting his old girlfriend. Later we see him married and with young children before the final events of the movie.
How much total time has elapsed between the opening scenes and the end?