In "Space Seed",Spock says something like "during earth's final world war,in 1993"
But in First Contact,Data can be heard saying,when the enterprise-e goes back in time to 2063"I belive we have arrived about 10 years from the third world war"which means that it was in the 2050's.
If I recall correctly, Spock didn't mention when World War III took place. He was refearing to the Eugenics Wars which took place in the 1990's. Also when Spock mentions the third world war, he dosn't give a date, he just says how many people were killed.
In reference to the "Third War", if you go by the Star Trek reference books and even statements made during TNG, the Third War happened in 2064, 4 years after TNG goes back in time. So just how did they arrive 10 years after a war that didnt happen for another 4 years? Oops...
According to the Star Trek reference books, Khan was born/created in the 1960s, and seized power over South Asia and the Middle East in 1992. World War Three lasted from 1993 to 1996 (when Khan escaped in one of those old fashioned sleeper ships. You remember then from the nineties, right?)
Q's recreation of a courtroom from the "post-atomic horror" is set at 2079 (and if the U.S. Flag had 52 stars until 2079, we must have been blown away that very same year).
As for everything we know about Zephram Cochrane, he launched the Phoenix in 2063, ten years after the end of World War Three (and two years prior to the S.S. Valiant's disappearance near the edge of the galaxy).
Advanced space exploration and colonization seem to start in the 2060s, which would coincide with Earth's first contact with Vulcans. (I doubt we could have built a fleet that quickly, so we must have borrowed some ships from the Vulcans.)
Confusing, ain't it?
Something that a lot of people don't seem to get is that the time line for our reality and the time line for "Star Trek" are two different things, not necessarily dependent on one another. For instance, the Star Trek back story mentions a "Eulogenics War" (or something like that) occuring during the 1990's. It never happened (because the story was created in the 60's). Also, in more modern times, the "Star Trek: Voyager" episode "11:59", which was actually produced in the year 1999, recalls the story of one of Janeway's supposed ancestors, who helps develop a giant shopping mall/biosphere thing called the Millennium Gate in the year 2001. Obviously, the producers of "Star Trek: Voyager" knew nothing of a Millennium Gate project in the year 1999, and the creation of such a thing off of short notice was highly unlikely. Yet they wrote this story anyway. Why? Because, the Star Trek time line and our own are not the same.
Oh dear, the curse of retroactive continunity!
The Character of Zephram Cochrane originally came from the Alpha Centauri system, and first contact with the Vulcans came about when a warp capable vessel detected a distress call from a Vulcan vessel(By the way, sublight travel between the Sol & Alpha Centauri star systems was commonplace !) . This was changed in Star Trek:First Contact! By the way, a Manned Space probe was launched to Saturn in 1996 (At Least according to my formerly official Paramount guide to the Star Trek Time line, published when the first Star Trek Movie came out)
Yours,