I have noticed that when people have scripted conversations on television shows, the average time of responses is shorter than in an unscripted conversation and complex questions are answered immediately. The delay time needed to formulate an answer in one's head is a variable that depends on a lot of parameters as
@phinds noted. It may be longer if one is not a native speaker of the language, if one tries to cover up the truth or remember the lies he/she has already told, if one needs time to think how to spare someone else's feelings, etc. etc.