Well, MB may know something I don't, but I have never known of a Haruka missing its scheduled arrival time by more than 5 minutes. I suppose that an unforseen delay could occur but Japanese trains are notoriously punctual. I wouldn't worry too much about a late arrival. You would most likely be fine on the 6:46 departure but I would probably use the 6:22 and spend the extra time at KIX having a last meal or spending the last of my yen at some of the shops.

JR