What about the knee? If you've played long enough, you start to get a grasp of how much time you have before hit stun wears off after you've hit your opponent. Just matching this timing with the time you need in order to knee is all you really need to know. Again, it comes down to accurate placement of your move, while utilising the insane speed of captain falcon.
I feel like captain falcon and marth kind of have a similar combo style in that you hit them, then follow them after you know which way they are going (essentially seeing their DI and then following). Marth needs this because he need to be in the right spot to get the right hits he needs with his sword (usually tippers, but not always). Captain falcon needs this because depending on how you control him, you can land in very different spots, and hit in very different ways (especially with his up-air). Done correctly, you can make sure to land in the best spots after each hit and have greater success with your combos.