How to manipulate time in unity?

hi, i'm trying to build time in my game which is 30 seconds inside my game equal to a second in real time. i've try to use the timer script and multiply it with 30 but the timer gone wrong at the 2nd minute..

here's the code which is count for real time :

 private var startTime;
 var textTime : String; 
 var myFont : Font;
 
 
 
 function Awake() {
    startTime = Time.time;
 
 }
 
 function OnGUI () {
     var guiTime = ((Time.time - startTime));  //i've try multiply this time with 30
 
   var hours : int = (guiTime / 14400) % 23;
    var minutes : int = (guiTime / 120) % 59;
    var seconds : int = guiTime % 60;
  
 
    textTime = String.Format ("{0:00}:{1:00}:{2:00}",hours, minutes, seconds); 
    GUI.skin.font = myFont;
    GUI.Label(Rect(600, 15, 100, 30), "Time : ");
    GUI.Label (Rect (600, 40, 100, 30), textTime); 
    
 }

i hope someone can help. thanks!

*sorry for my bad english..:p