That is a great question. I could get away with saying that the setting has not changed at all. Normally setting is time and place. The story starts in the United States in the year 2055. The story ends in the United States in the year 2055. The setting has not changed.
But that's cheating. Eckels comes back to a very different country after his dinosaur hunting, butterfly killing adventure. While the country is still the United States, the elected president is completely different. The laws of the country are completely different. The system of government is completely different. Even the language is different. At the beginning of the story the reader learns that Keith won the election. Everybody is happy, because they think that Deutscher would have made a terrible president.
"We're lucky. If Deutscher had gotten in, we'd have the worst kind of dictatorship. There's an anti everything man for you, a militarist, antiChrist, anti human, antiintellectual. People called us up, you know, joking but not joking. Said if Deutscher became President they wanted to go live in 1492."
When Eckels arrives back in the present, the reader learns that Deutscher is likely the president of a very different United States. We learn about this likely shift by seeing the change in the Time Safari welcome sign.
TYME SEFARI INC. SEFARIS TU ANY YEER EN THE PAST. YU NAIM THE ANIMALL. WEE TAEK YU THAIR. YU SHOOT ITT.