League of Legends (LoL) Question: Zilean's Time Bomb Stun Problem

i think its the travel speed of the Q that's messing you up it has a very slow travel time like gragas Q/R making it very difficult to land on the champion when you do that and I believe that it has a slight delay when you do the W(probably because of an animation) so that might be it. With enough practice it might become easier to do you just need to practice with a moving target to get the timings down.