How long should i strech a day to kick hard?

Im not very good at my kicks and a guy at kickboxing was kinda mocking me about it saying that he couldn't feel my kick for crap with the kicking shields and he was holding it with one hand cus he couldn't feel it . so imma prove him wrong and i heard that if u strech ull kick higher and harder so can you please tell me for how much time a day should i strech and for how many days weeks months etc.