Late autumn, early morning.
This one has a few instances of the titular line.
The most significant one is right after a significant bit of dancing:
"Very well", said Emperor Te-kuan. "I will be guided by you." Said it on the grass, autumn, under the river of stars.
But the use of the title that I think makes the statement the book is trying to convey is on page 424:
It goes back too far. We might as well blame the river of stars, or heaven.
And on page 578, our author maybe reminds us he is there:
The river of stars, in the legends of Kitai, lies between mortal men and their dreams. There were no stars visible in the sky yet that autumn day, but a poet might have placed them there.
This book is really interesting, especially for the way it treats the arc of the patriotic hero. It's definitely not how Hollywood would tell the story. That said, I think the preceding book, Under Heaven, is still the best book I've read in two years.