Nah, you can do it at any attack speed %.
If you want to look into it further i'd suggest searching youtube for a guy called Lastshadow9, he has coached a few proffesional teams and was Diamond 1 in the Korean scene, also working along side some of the League organisations there, his youtube channel consists of him and a player going over a recording of a game he played and then they analyse it, if you look for one of the Draven players he will go into great detail about playing him effectvely, and how to alter the landing locations of the axes, i've watched it numerous times and it's helped me become a great Draven player, the way i described it is exactly how it works, but if you like draven then i would watch that video. Also if you search CJ Emperor from last year he was/is in the OGN scene, excellent draven player also DB Hosan from 2013, another top class Draven player!
(just realised how much i rambled on there, hopefully it helps)
EDIT: Take Attack speed Quints, AD Reds, scaling MR Blues and Scaling Armor Yellows.
Add me, summoner name is Proxeum