I believe the first-party primary domain of the app will never have its data wiped — though the article could certainly be clearer on the point. What would be cleared in that case would be any other domains — if there's also a "Visit Zombo Facebook" link in there, and you only looked at Twitter for a week, the Facebook cookies would be wiped.
Then the next few times I switch to the app, I don't launch it from scratch, I just look at the twitter.
Then I've gone seven days inside the zombocom app without touching their actual domain.
Does everything except the twitter cookies get deleted?