Reset a timer?

I have a timer which counts down to 0 before an explosion happens. What im basically using it for is to keep the enemy on screen for a short amount of time and then get rid of them. I have this working but it only works once. Here is my code:

 function BlowyUppyThing()
 {
     if( --BlowyUppyTimer == 0 )
     {
         CancelInvoke( "BlowyUppyThing" );
       if ( BlowyUppyTimer == 0 )
         {
             Instantiate( explosion, transform.position, transform.rotation );
             audio.Play();
             var position = Vector3 (Random.Range(-6,6),Random.Range(-4,4),0);
             RespawnDelay();
             transform.position = position;
             renderer.enabled = false;
         }
     
         
     }
 }

But, as said before, i need some way to reset the timer so that it constantly works, rather than only working once.