How to do this mechanic?

I’ve been wanting to know how to do this or if I am just over thinking it. How does he go from sitting on his a** to jumping in the air in a split second, everytime I try it takes an extra split second to stand up then jump, but these guys do it instantly. I play on tactical and do the slide / prone with my right stick, do I just have to be faster and mash jump button or is there a setting?