need help with variables

so im making a mod with a item that allows you to heal yourself when you click it and then it will go onto a cooldown of three minutes but the problem is you  can still use it in that time so my way of fixing that is to make a variable to act as a cooldown but i dont really know what im doing when it comes to variables at all so if its no a problem to you can you please tell me how i should approach this situation.  https://imgur.com/a/d4wjHGM