"Not very precisely. With the number of years he was gone on Earth, though, it should've been a long while... longer than the White Witch actually reigned, I think, if the time difference is always exactly the same. So I guess it isn't. Maybe, I don't know, maybe the wardrobe or whatever affects these things will make long visits short if you return quickly but gives up on you after a while if you stay indefinitely. In which case we've been gone for years, probably."