Cool from the get go! Your vocal really is great and the bgv's, and the mellotronishness, it's just a really great re-creation of the Beatles vibe. And then you add some effects here and there, it all fits.
There is no reason you shouldn't let it run long, given the subject matter, if that is what obviously pleases you!
But from the emotionally-neutral listener's perspective, if something is 5 and a half long, maybe a different part in the middle, or an interlude, or a drum solo, or something to break up the pattern for a bit would be a thought.
Or my attention span is just too short. And you are writing this for yourself, so there you go.
It's a great choice of song and you did a great job bringing the past to life.
cheers,
-Tom