I cant get this timer to start when this bool turns true?

I cant see how the timer works with the startTime = Time.time; and var guiTime = Time.time - startTime;

I just dont understand that, so I dont know how to make the timer start when GameStarted is true, instead of starting when the game loads. I tried enabling the script when GameStarted turned true, but the timer starts when the game is started for some reason. Thanks in advance.

 private var startTime; 
 private var restSeconds : int;
 private var roundedRestSeconds : int;
 private var displaySeconds : int; 
 private var displayMinutes : int;
 
 var countDownSeconds : int;
 
 function Awake() {
 startTime = Time.time;
   }
 function Update() {
 if (GetComponent("HS").GameStarted == true) {
  // Start timer here
 }
 }
 function OnGUI () { //make sure that your time is based on when this script was first called //instead of when your game started 
  
 var guiTime = Time.time - startTime;
 
  restSeconds = countDownSeconds - (guiTime);
  
  //display messages or whatever here -->do stuff based on your timer
  if (restSeconds == 60) {
      print ("One Minute Left");
  }
  if (restSeconds <= 0) {
  restSeconds = 0;
      print ("Time is Over");
     GetComponent("HS").TimesUp = true;
      GetComponent("HS").GameStarted = false;
 
  }
  
  //display the timer
  roundedRestSeconds = Mathf.CeilToInt(restSeconds);
  displaySeconds = roundedRestSeconds % 60;
  displayMinutes = roundedRestSeconds / 60; 
  
  text = String.Format ("{0:00}:{1:00}", displayMinutes, displaySeconds); 
  GUI.Label (Rect (400, 25, 100, 30), text);
  }