There's a reason why title fights are 12 rounds! But I think that Khan was just messing and didn't expect people to actually take it seriously. But to be fair, if I was Khan or his trainer or manager, you could do a lot worse than going and sparring with PBF for a while. Give's you a glimpse at what it takes to be a world champ at what its like at the top of the mountain. Also PBF is an absolute professional when it comes to his pre-fight prep/training, and hopefully that would rub off on Khan.