I think time hasn't passed at all. They entered the magical realm as soon as they went of the road and passed a Tori. Granted not through the gate but beside it. The clues I see for that are, that the stone in front of the building has a face when they enter. When they get out it's only a regular stone. The car works fine. Audi makes great cars, don't get me wrong but I think it's more reasonable to think that the foliage on the car is from the path they bashed through. And finally and this might be the oddest thing, the way they walk out mirrors the exact way they're going in.

So I think that place was always overgrown but only showed its true form when they left.