I wonder how much time you would end up with if you added up every reference to the passage of time in all of the novels, episodes, and comics for TOS.
I undertook that exercise a few years back. OK, in 1986, which was what, 27 years ago?
At that point I concluded that there were already too many episodes/books/comics than could comfortably fit in a single five-year mission.
I believe that was one of the reasons the "Pocketverse" of the '80's assumed a second five-year mission between "Turnabout Intruder" and TMP. (Well, that, and as a way to explain why Shatner, Nimoy and everyone else had clearly aged a decade in ~3 years.)
I imagine that a similar exercise undertaken today would have to pack ~40 years worth of adventures into a five-year mission. As someone commented, that way lies madness.