Ah. From what I've gathered it's not as if you can actually peruse any dossiers / intel sources in the middle of a conversation...
So it's immersing you in the concept that a spy in the field will have had to have read such things before hand and can't just pause a conversation and do the "hang on, before I answer you I just need to access email to see how you'll best take this.."
It'll be based around the idea that you'll have had a source that implies "Oh yeah, Sie, she's a serious gunbunny. Doesn't like whimsy, but gets on well with more forceful types". So it'll stick in your mind that Sie would react to aggressive responses better then suave. 8 seconds might not sound like much time, but it can stretch out awhile when it's just that mental juggle of memory and a one/two button press.
To me the moment a character turns up, even before actual dialogue opens up, there's that mental run through of what you know about them, what you want from them, and seeing what might be needed to do the mission.. so you'll be thinking about stances before they open their mouth.. which is going to add to the timer that'll click on when they actually expect a response.
And that's the other side of it, the timer won't be starting up until they've finished speaking.. so before they're halfway through whatever dialogue they have I'd expect to be choosing a stance.. (I mean sure, it wouldn't be a final choice until they've finished and I've heard it all.. but it'll probably be close).
But hey, I recognise that not everyone will think or feel that way.. so it's just my two cents worth