Do we actually know how long it took to make that trip, in days / hours / minutes / seconds?
The big piece of evidence point to the Earth-to-Vulcan travel time being unreasonably short is Sulu telling Pike they've reached maximum warp, which starts an unbroken stretch of action that goes all the way to the
Enterprise arriving at Vulcan. There is a time gap just before that, when Kirk passes out, which lasts at least long enough for McCoy to change uniforms. Kirk could be unconscious for seconds, or he could be out for days, but the kicker is that they ship probably should hit top speed earlier than the last couple minutes of its journey unless the entire journey only lasted a few minutes. It's hand-waveable, but awkward.
No, the really hard one to figure out is STID, where the trip from Earth to the edge of the Klingon home system takes an ambiguous amount of time, but the trip back seems to cover only a couple minutes, unless, again, McCoy waits several hours for no reason before checking out Khan and telling him they've fled the Admiral's ship. Worse than that is that is the dreadnaught knocks them out of warp inside the orbit of the moon; one, the
Enterprise really should've already slowed down if they were that close (it's like being run off the road in a 90 MPH car chase down the interstate, and crashing into your own mailbox), and, two, the Admiral has already failed in keeping Kirk from getting to Earth and telling Starfleet about his dastardly plan; even if communications are jammed, they can still just look out the window and watch Admiral Robocop murder their golden-boy with a mysterious, evil-looking starship.
Beyond is a bit better, if only because nobody does anything while the ships cross through the nebula aside from crossing through the nebula, so it's easy to imagine it takes as much time as seems reasonable to cross the nebula.
