How to Create a Countdown Timer and Show Current Time in Unity3D

#pragma strict
 
 var timer: float = 70;
 var isFinishedLevel : boolean = false;
 public var displayText : UnityEngine.UI.Text;
 public var timeText : UnityEngine.UI.Text;
 
 var minsDisplay : String;
 var secsDisplay : String;
 
 var mySeconds : int = 0;
 
 private var oldTimer : float;
 
 function Start(){
     oldTimer = timer;
 }
 
 function Update()
 {
     if (!isFinishedLevel) {
         timer -= Time.deltaTime;
     } 
     
     CurrentTime();
 }
 
 function CurrentTime() { 
     var dt : System.DateTime = System.DateTime.Now;
     var h : int = dt.Hour; 
     var m : int = dt.Minute; 
     var s : int = dt.Second;
 
     timeText.text = h + ":" + m + ":" + s;
     
     if(mySeconds != s)
     {
         mySeconds = s;
         Timing();
     }
     
 }
 
 function Timing()
 {
     if (timer > 0) {
         //var minsDisplay : String = parseInt( timer / 60 ).ToString();
         minsDisplay = parseInt( timer / 60 ).ToString();
         
         //var secsDisplay : String = parseInt( timer ).ToString();
         secsDisplay = parseInt( timer ).ToString();
          
         if ( (timer - ( parseInt(minsDisplay) * 60)) > 10 ) {
              secsDisplay = parseInt( timer - ( parseInt(minsDisplay) * 60) ).ToString();
         } 
         else {
             secsDisplay = "0" + parseInt( timer - ( parseInt(minsDisplay) * 60) ).ToString();
         }
         
         //displayText.text = minsDisplay + " : " + secsDisplay;
     } 
     else {
          timer += oldTimer;
     }
     displayText.text = minsDisplay + " : " + secsDisplay;
 }