jump startup happens when you finish your input so it has nothing to do with that.
it just your execution , so just work on that. Maybe because you think that it has anything to do with that so it hinder you from doing it correctly.
I don't understand why you wanna do IAD jC anyway with either haz or jin , IAD usually is usually being used for crossup jC isn't a good move to cross people up maybe sometimes you want to do long range poke with IAD jc with jin, but it's not really good to do that, you can just jump instead.