Most of episode 6's bump should be from episode 5. "The Kiss" should affect episode 7 ratings the most, and episode 8 ratings will hopefully show the staying power of the bump.
---- Update -----
Well with the new info about a 2nd Kiss dubbed "Cola Kiss," I feel the writer is taking a very aggressive approach (which I am all for) right now. In fact, episodes 5-8, if done correctly have the potential to make this drama a ratings hit, but it also has the potential to way under deliver leading to huge disappointment among the viewers.
As I said above episode 5 caused most of the episode 6 bump. The “Ice Cream Kiss” (made up name to differentiate from the 2nd Kiss) at the end of episode 6 is the shock scene, I am a guy and even I thought it was intense, that should get tons of buzz prior to episode 7. So, the total viewership should be up again for episode 7, so if that episode can at least deliver above average quality. Then it should setup everything nicely for the “Cola Kiss” in episode 8 to hit at least a home run if not a grand slam!
*Just in case any reader does not get the baseball analogue, a home run is worth 1 run, and a Grand Slam is worth 4 runs. So, it is much better.