How does the speedboost work in world 5 in BBF's wr? Timestamp included :

I'd like to know frame windows/just in detail stuff about how the trick works if possible ^^

Is there any explanation/video on how to do the kirby jump, I am using the same starting position for the first jump as BBF in his WR, I'm able to get it at like 20% consistency, and wanted to know if there's any other visual cues/frame windows, or extra info i'm missing. (something having to do with using/not using certain checkpoints)