Here’s my theory.
If it’s the first time you’ve run a title, 30 seconds will not work. However, once you have listened to a title for a sufficient amount of time, the subconscious remembers the entire script. Listening to 30 seconds “reignites” the memory of that script as if the entire thing had been played, and thus you get similar results (not the same) as if you listened to the entire thing.
Think of it as the same phenomenon that occurs when you look at a clip of your favorite movie on YouTube. If you’ve seen that movie enough, you will be able to remember exactly where that clip falls in the movie, what happened before and after that scene, etc.
You no longer need to watch the entire thing to remember what it was about and its underlying theme.
Vader reveals to Luke that he is his father. You remember Luke’s reaction, and how that revelation changed the rest of the overarching story. You remember how you felt, and what you gleaned personally from the story.
Every now and again, however, you enjoy watching the entire thing as a reup.
‘Tis the theory.