Hello there sspeed.
Well, you will need to know the name of the animation.
For example, could be attack01 or spell01 etc.
You could check it using the cutscene editor tab.
After that you need to open the immortal actor and modify the event.
Look for the event that trigger that skill and animation.
Once you find it, you just need to modify the time.
I am currently out and can't open the editor, so i can't include screenshots.
Hope that helps.