Need some help with farming mod..

Hello

I need help because I don't know how to make one procedure.

Because in my mod there's new cow (the cow from my mod has the same model and texture but works differently).

I have made procedure that checks what you have in hand.

If you hold in hand right item cow gives milk. 

There's no delay. So player can milk any time he wants. I don't know how to make delay.

I want to do delay ex. 500 tick. So Player must wait 500 tick before he will can milk cow again.

Is this possible?

Sorry for my english. I'm from Poland

Thanks for any replies.