Buffs and Instants question

This isn't a tanking specific question but I play a tank and the self buffs that we get as tanks are very important for mitigating damage. Basically I am a little confused on how all the non GCD abilities work. The first instant that I use usually goes off without issue but after that it gets annoying. Is there a hidden cool down between using instants or is it a server lag issue. When I try to work multiple instants in to my rotation between GCD skills it gets even more screwy and I just end up mashing the button until it goes off. If someone could explain how it works or give me some tips it would be appreciated.

I was curious about this as well, having the same issue

There is an animation lock on many abilities. If you try to use anything while the animation lock is happening (it's generally a half second to a second after the ability is invoked), nothing happens. There's no indication of the cooldown, other than the fact that you can't get anything to happen. I haven't done a rigourous study of them, but they seem to be most common in your main attack moves.

If you are in the middle of any attack animation, you are incapable of activating any off-GCD abilities because your character is locked into that animation. As such, if you're hitting an off-GCD ability before you hit an attack button, you're queuing up the off-GCD to activate before the next animation so it resolves beforehand. If you use an off-GCD afterwards, on the other hand, it won't activate because you're already occupied. The only way to use multiple off-GCDs in quick succession is to not attack while you're busy clicking the lot of them and, even then, you'll have a slight wait between as each of their animations resolve before you can activate the next one.