I've only played mounted combat as a hunter but often times i will click on a skill and have to wait a good 5 seconds before it gets used. Some i give up waiting and use a different skill then click back to the skill i was waiting for and it fires.

Is this a server lag? or an induction time putting in place under certain circumstances?

My kill shot skill can sometimes fire right away when i click on it or it takes 5 seconds to fire and during this waiting time im just circling my mob getting hit.