It happens again! This time in 'The Age of Miracles' by Karen Thompson Walker, p. 93:
'I wanted to think that somewhere on the other end of time, a hundred light-years from then, someone else, some distant future creature might be looking back...'
The author might say that it's intentional, but that would be very lame.
Yes. Once in one of our classes we were supposed to write a short story and one of my classmates had used 'light-year' exactly the same way as in the text you mentioned. When I said that 'light-year' is measuring distance, he said, "I now. But this is fiction and I've used it for time'! His story was, in fact, a short short story and the only way I could think was that he had made a mistake.( The definition alteration had not been well justified.)
Yeah, you can't change the meaning of words just because you're writing fiction. You can make up words, if you want to, or terms. You can even, if you want to be confusing, use an existing term and give it a new meaning. But in that case you must make it clear to the reader that that's what you've done; otherwise the reader will persist in believing what we actually do believe, that both writers simply made a mistake.
And anyway, how would "a hundred years from then" quality as "the other end of time"? (Just being querulous.)
Late in the book, the father of the teenage girl uses it for distance.
I almost see the author's sly smile.
Anyway, it is a good sci-fi, just out, first book by this author. (But not if you don't like sad stuffs.)