What are you looking at? And how are you looking at it? I don't want to give a speculative response if I can give an informed one instead.
In the first place at the NPC behaviour in game, regarding their character scripts: when NPCs are supposed to start an automated dialog or display voiced text according to the script and if these actions appear in game as expected; from what I see, voiced text (automated dialog and voiced text display) can 'loop' (i. e. be started again) without delay, so I concluded there is no delay between start times or - maybe - to short to be noticed. I haven't found a story script that would allow to set delay times for NPCs, so if such a function exists it's probably hardcoded. - But even if there was such a function the 'issues' I described above would remain (some extra actions necessary to 'compensate' the silence in situations that aren't supposed to be 'silent', extra 'silent actions' between voiced or more lively actions, and no fully individualized frequency of voiced text loop).
What do you have in mind when you speak of 'delay between start times'?
