I would just like to point out that the beginning and end of Spirited Away creep me out in the most delicious way possible. I’ve always been a fan of fairy tales, and not just the Grimm and Anderson stuff, almost all my life. Like the honestly faerie court stories.
Themes you see in those reflect strongly in this movie, and comparing them side by side just makes it that much more stark.
Often times you hear that if you get sucked into the fairy realm, you shouldn’t eat their food. It gives them power over you. More often than not, heroes finally escape the fairy realm after what they perceive to be a very short time (a night or a week)…

…only to find that seasons or years have passed.

‘Hey, it’s all dusty in here. Is this someone’s idea of a joke?’

This always freaked me out a little as a kid. Like the OP, I couldn’t help but wonder how long REALLY passed. I always pretended it was something like a week but… Judging by that moss, I can’t say for sure.

A week? Try much MUCH /MUCH/ longer. The plants are a good indicator but a better one is the statue. We’re seeing it from the same angle in each shot. Look in the first one before she enters, it’s not NEW but you can tell what it is.
Now look at the second frame. It’s so eroded it’s just a dull, flat stone.
That thing is solid stone, that must have taken up to, if not more than, a DECADE to wear down that much.
Not to mention that there are new trees next to the car. Just remember how long it actually takes for trees to grow real quick.
Evidence is suggesting they were in there for maybe around 20-30 years.

What always struck me as particularly odd was the building. Apologies for lack of screenshots, I’m not at home so I don’t have access to my copy of Spirited Away, I’ll add them in when I can (or if someone else can grab them for me that’d be swell).
Look at the building they went into, and the building they walked out of. They entered a red building which the father comments on as being “fake” and made of plaster. They exit a building made of stone. It’s possible that the plaster building was laid over the stone building (as the plaster building’s doorway is narrower and such) but if it had fallen apart over the years you’d see evidence of the remaining plaster. Not to mention when they exit the building on the other side some of the plaster has fallen away and the stone beneath is red and brick-like. not grey stone. 
And the building her parents are waiting outside when Chihiro goes to meet them after leaving Haku looks different from the one they exited at the beginning of the film. The most noticeable difference is it’s missing the large room with the benches (which was just inside and not down a hall) and they don’t pass through that room at all on their way back. On the way in, the camera lingered on three doors as Chihiro was looking back at them (which is interesting but I’ll get to that in a second), and it also lingered on a sundial (you know, a thing that tracks time). They spend too much time in that room for it to be inconsequential.
When I first watched it I was actually expecting them to have to try to remember which door they came through at the end - which I had forgotten about by the end of the film, but every time I watch it I always have a similar thought despite knowing how the film ends. The outside of the building they enter looks different from the one they exited at the beginning of the film, but the most telling factor of it not being the same is it missing that room, and us missing a scene in that room as they left.
And I find that so interesting because as they walk down the hall the scene is practically a duplicate of the scene of them walking in. The same actions are taken and the same lines are said, the father tells them to watch their step, the mother tells Chihiro to stop clinging to her because she’ll trip - I’m fairly certain the phrasing is exactly the same, and the animation might be exactly the same, too, but I can’t check. The biggest difference is that at the end of the film Chihiro only looks back once they get out, while at the beginning she has reservations about going in, looks back at the statue, looks back at the three doors, and looks back when the wind blows at her out of the building. 
I’m NOT AT ALL SURE what all of that might mean, but there are a lot of differences there. Is it just that time passed? Have they been shoved out into a different place altogether? I don’t know but I sure do love thinking about it every single time I watch this film.
Hello :3 I love your Madoka cosplay and I was wondering if you could let me know wear you bought the wig from. If you can tell me, Id'e really appreciate it! Thanks a bunch, friend X3

Sorry I bought it a long time ago and can’t remember the sellers name but my favourite wig seller on eBay is jcpunk I have bought 4 wigs from him and I loved them all, he ships relatively fast too. Hope that helps :)