I hate the thought of posting a story that could have been exactly what I wanted it to be, if only I'd had more time.

If only the prompt had been about the interaction of side character C & D instead of pairing A and B... ;)

prompts don't necessarily have to appear in the context of an exchange

So true, but if a fandom has become very, very quiet that's often the only place where prompts sometimes still come up. I admit, I often browse prompts but then decide just to write them without participating in the challenge, thus taking the time restriction off. I have too much deadlines when writing research papers already. ;)