Scratch what I said before, I'll walk you through how to do it.
1st, Create a new "Item Strength Gain".
2nd, Set the "Data - Strength Bonus" field to 0.
3rd, Set the "Stats - Cooldown" to whatever time you want, 0.1 being the lowest and fastest time.
4th, Go to the item you want to change the cooldown time for.
5th, Add the ability you just made to the "Abilities - Abilities" field.
If you want to use the same cooldown for more than one item just add the same ability to the other item's ability list. Also, you can change the effect the ability does by changing the "Art - Target" field to whatever you want it to look like and setting "Art - Target Attachment Point" to (my suggestion) origin.
@Mr Bean, nevermind you were right. Though you don't have to make one for every item, you can just have one if you wanted.