If you have to purify or perform any other action besides one that directly interrupts the limit break it will be too late, it's that fast.

Btw even though it's not written in the description for fetter ward it apparently also nullifies knockback. At the very least it nullifies the knockback from white mage fluid aura.

Whether it only works on whm fluid aura since it also tries to bind u or it nullifies all forms of knockback I am not quite sure. Hard to test it since can't always predict when people will try to knock back u but if anyone knows off hand I and many other people would appreciate the info.