For me, it almost never works out well to give them any words to work with, because the depth of their delusion/narcissism will just allow them to stoop to whatever level is required to give an answer consistent with their worldview.

If I were you, I'd do the 5-ish seconds but then instead of finishing with words, give an incredulous chuckle. As in, "Wow, I can't believe you really thought that was OK to say out loud" or "what you just said was so ridiculous I can't come up with any other response than laughter". Then redirect your attention immediately. That way, if they try to engage you further, you can hit them with the "are you still talking?" attitude/body language. By actually responding (with words) you're on some level giving them permission to further engage and acknowledging the validity of the conversation.