To activate an ability from a gameplay effect, I think you can use the triggers of that ability, which can watch whenever a tag is added to the owner.
For the 1 second cast time, in your ability, I would add a WaitDelay task of 1 second right after your ability starts, from which you would plug your gameplay code. I would also add a WaitInputRelease task to cancel if the player released the button before that 1 second delay for example, if you need.
I think that would be a good starting point (I don’t have a lot of experience with the system right now)