Hi, all. I have a ticket on G16 tomorrow/today (11a train from SH to BJ). I'm thinking about refunding it because my best friend just showed up in town somewhat unannounced, and I'd like hang out with him. Since I've already refunded one HSR ticket within the past ~2 weeks, I KNOW that this can only be accomplished at a train station (any of the big ones). However, I never bothered to seek clarification about whether this can be done after my train departs. And, if so, how much time I have before the ticket goes "poof".

If I have to drag myself to a train station at 10a, I'll probably end up just taking the darn thing.

BTW, this whole "go to train station to cancel" drill is major thorn in the side of my beloved train, but if it turns out that tickets retain value for a reasonable amount of time (even 3 days), I'll be able to overlook this shortcoming.