After reading this thread I decided to book my ticket for the weekend at an agent instead of risking showing up at the station. The online services also seemed to have Sunday pretty booked up for the return. I am picking my tickets up tomorrow. I think that they charge 10 RMB each way extra, but that seems a pretty good deal based on this thread!
Of course she spoke no English and my 3-lesson-Mandarin is limited to times and days with terrible pronunciation (it took a calendar and welcome patience for her to understand that I meant Sunday - I just can't get that 'ri' sound yet!) so we well see where I end up

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I'm also going to show up super-early just in case - I will bring a book

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Good luck to the OP!