My personal standard for an RP post, both giving and receiving (make a joke and I'll tear your face off), is roughly 2 minutes, and that's assuming the post is at least 1 full chat box in length.
I don't mind longer RPers as long as they can put out quality posts. I like to provide great detail with unique word choice as opposed to just throwing lines out left and right. When I'm RPing, I'm writing - not chatting - regardless of what the RP is actually of.
I understand some people want faster posts, but really give strangers more than 30 seconds to reply. They might be cooking up a post that's not "Hey how are you?".
It happened to me just earlier today, actually. Someone walked up to me, asked me a 1-line question, and I was working on responding with a decently sized emote. A few seconds before I pressed enter, the guy was already wandering off. It was barely even a minute, at most. Rather irritating.
See also, massive posts that take up entire chatboxes. Hate to break it to the people who do them, but they actually aren't that good as a stylistic method. Break them up a little, post an action, then a portion of speech. Let us read a part as you type the next. Anyone who uses 'I have a lot to type' as an excuse is, frankly, doing it in a way that makes me bored and less interested in what they ultimately have to say.
The issue with that is, how do they know when you've stopped typing? It's frustrating and/or disappointing when an idea you have, or a motion you're making, suddenly gets cut-off because someone decided to throw their own post in as you go to put in the finishing touches.
I don't have any add-ons or anything that lengthens the chat-box. For longer emotes, even if the sentence is officially finished by the end, I put in a few dashes at the end to signify that there's more to it. On VERY rare occasion do I actually post something else before my emote is "complete" if there's no hyphens in the previous one to signify that I was continuing. In that regard, you're reading a chunk of it while I'm working on the rest.
I like posting, and I like reading, quality emotes. I don't mind if it takes a little more time. Even if you can dish out emotes in the blink of an eye, if they're 1-2 lines and lack detail, I'll probably be bored and less interested no matter how much we cover.