This too has been my main prob with tanking so far.. when I'm asked to both hold aggro (main tank) and use stun to stop a bosses abilities because there is no offtank PLD to do it. Without exception there are going to be times when the boss starts casting the ability right after you've just used an enmity ability.. and that's it you can't hit the stun in time because of GCD.

Not all bosses have predictable cast times for their abilities. Dhorme Chimera throws them up randomly it seems to me and often. Not sure but lag might be a factor too.. sometimes i notice the bosses casting bar moves or jumps faster than other times.

Anyway, I'm mainly looking for specific info on how the pros do it. Ability hotbar placement, shortcut keys, what to look for, etc? Specifics
I'm still using the mouse to hit my abilities. Do i need to study each fight like a freak?