Change score based on time remaining.

This questions a little tricky to word but i would like to make it so that when you get to say 30 seconds left on the timer, the amount of points you would get from shooting the blocks decreases by 1 point. So you start by getting 5 points and eventually this decreases the more time you spend playing the game.

This is my timer script.

var Counter : float;

function Start () {

}

function Update() 
{
	Counter -= Time.deltaTime;
}

function OnGUI ()
{
	GUI.Label (Rect (Screen.width / 4 - 50, Screen.height / 4-50, 100, 100), "Time Remaining: " + Counter);
}

This is my score script.

function OnCollisionEnter(collision : Collision)
{
	if (collision.collider.tag == "ammo")
	{
		Debug.Log("Score!");
		ScoreScript.Counter += 5;
	}
}

This is my block behaviour script were my blocks change color and eventually destroy.

function Start () {
}
function Update () {
}
function OnCollisionEnter(collision : Collision)
{
	if (collision.collider.tag == "ammo")
	{
		if (gameObject.tag == "whiteBlock")
		{
		transform.renderer.material.color = Color.red;
			gameObject.tag = "redBlock";
				Debug.Log("Red Block Created"+collision.collider.tag);
		}
			
		else if (gameObject.tag == "redBlock")
		{
		transform.renderer.material.color = Color.green;
			gameObject.tag = "greenBlock";
				Debug.Log("Green Block Created"+collision.collider.tag);
		}
		
		else if (gameObject.tag == "greenBlock"){
			Destroy (gameObject);
		}
	}


	
	
	//Debug.Log("Collision Detected by "+collision.collider.tag);
}		

How would i go around doing this task? any help would i would be grateful!

I would do something like this:

var scoreMultiplier = 5;

function Start () {
     InvokeRepeating( "DecreaseMultiplier", 30 , 30);
     //You could easily set this up as a coroutine if you wanted variable times.
}

function DecreaseMultiplier () {
     scoreMultiplier--;
     //Possibly clamp at 1pt.
}

function OnCollisionEnter () {
     score += scoreMultiplier;
     //basically the same as yours, just with a variable.
}