I don't think there was much support for the idea that TMP would be in 2273 until the Okudas suggested it in their Chronology. Back when the movie was made, the idea of "Star Trek happens 300 years after the airdate sharp" was going strong among the fans, and TMP was made by fans, sort of. And the movie itself contains the tidbit that it happens over 300 years after the launch of Voyager 6, while Voyager 1 and 2 went up no sooner than 1977.
OTOH, five year missions are problematic overall. Supposedly, nobody performed one of those before Kirk, because he lists this as a unique qualification for challenging the mystery cloud - even though Earth, the de facto home of Starfleet, ought to have thousands of officers qualified to command a starship and not hobbled by being Chief of SF Operations. Certainly Kirk didn't perform two of those before TMP, because he only refers to one.
That there would exist a "five year mission" is a concept only ever mentioned in ST:Into Darkness. There, Kirk is excited that this is how long he will be spending in deep space if/when chosen for the mission. Elsewhere, five years apparently is just what the mission clock says when Kirk, for unrelated reasons, says it's time to go home - and is only commented on ex post facto.
Timo Saloniemi
OTOH, five year missions are problematic overall. Supposedly, nobody performed one of those before Kirk, because he lists this as a unique qualification for challenging the mystery cloud - even though Earth, the de facto home of Starfleet, ought to have thousands of officers qualified to command a starship and not hobbled by being Chief of SF Operations. Certainly Kirk didn't perform two of those before TMP, because he only refers to one.
That there would exist a "five year mission" is a concept only ever mentioned in ST:Into Darkness. There, Kirk is excited that this is how long he will be spending in deep space if/when chosen for the mission. Elsewhere, five years apparently is just what the mission clock says when Kirk, for unrelated reasons, says it's time to go home - and is only commented on ex post facto.
Timo Saloniemi