How to to do a progress bar wich scale down in 6 seconds ? (timeScale used)

So for exemple i want to do a timer wich count down 6 to 0 in seconds. At 6 the progress bar is full at 0 it is empty. In the meantime i use timeScale to slow down the time but i still want the timer counting down real 6 seconds.

   private float timerPercent = 1f;
   private float timer = 6;
   public Texture2D barTimer;
     
 
 void OnTriggerEnter()
 { 
    Time.timeScale = 0.1f;
 }
 void OnGUI() 
     {
         if (patternActivate)
         {
             GUI.BeginGroup(new Rect(Screen.width / 2-200, Screen.height / 2+25, 400 * timerPercent, 10));
             GUI.DrawTexture(new Rect(0, 0, 400, 10), barTimer);
             GUI.EndGroup();
         }
        
     }
 
 void Update()
 {
  timer = ?
  timerPercent = ?
 
 }