[BehaviorTree-AI] How do i make a Cooldown with a random timer that is set up everytime?

Im setting up a cooldown decorator. And need it to set its time to a random time between 30s and 60s, everytime it fires.
So for example. You fire it, then the cooldown sets to 47.s (random).
Then in 47s it will fire again. Then it sets to another random value like 32s.
Then the next time it will fire is 32s.
I know this requires a custom Cooldown decorator. But i cant even see how the original Cooldown decorator is done…