how do i create a potion effect whose effect has a cooldown

I want to create a potion effect accecible with a chestplate whose effect is that whenever an entity wearing that chesstplate is hit it will explode but will deal 0 damage to the entity wearing it. This effect has a cooldown of 5 seconds so how do i make this effect.

My current code - https://imgur.com/a/bH0XBhf