When does an attraction begin? Is it the moment you step onto a moving vehicle or the show starts? I think in the past that was true.
For all of you pining for the EPCOT Center of old, think of how engaged you feel slowly moving through the Living with the Land queue and you'll know how these rides handled their act ones. I remember thinking how The Living Seas queue stood out at the park as it wasn't a switchback and there was actually stuff to look at while you waited (besides a mural or carpeted walls.)
For myself, once immersed in the theme and story of an attraction, I feel we've begun. Nowadays that happens well before the (short) ride, at least with the bigger attractions. If the Flight of Passage queue was navigated by a slow moving omnimover with a dry narration telling me what I was looking at- you've basically got something on par in breath and scope of an EPCOT Center attraction (albeit with only one animatronic, but that garden area between the waterfalls and floating mountains trumps all as far as I'm concerened.)
Tower of Terror is a great example. From the time the tower looms over me in the garden I feel like I'm in it. I'm not only fully engaged, but am absorbing the story. The lobby and boiler rooms are more show-scene than holding pen. The ride itself is short, but my sense of attraction time is considerably longer.
Outside of the argument of location, I'll say once the Guardians's queue has me fully immersed in that world and the story begins to unfold, I'll likely consider myself on the attraction.