In the final conversation between Jack Weil and Bobby Duran, Jack refers to the Butterfly Effect as if it was already theorized and calculated. This is supposed to be the following days after the Cuban Revolution blasts, in early 1959. Although the idea of the ripple effect exists since before, the way Jack refers to it should only be possible to know after that, as related to the work of Edward Lorenz. This mathematician and meteorologist wrote a paper for the New York Academy of Sciences in 1963 noting "One meteorologist remarked that if the theory were correct, one flap of a seagull's wings could change the course of weather forever." In later speeches and papers, Lorenz used the more poetic word butterfly.
The bullet hole in the windshield of Jack's Cadillac has long cracks radiating from it in all the scenes in the country, but when he returns to Havana, the cracks are gone and only the bullet hole is there.