How to WaitforSeconds a GuiButton ?

Hi, little problem to understand the answers already posteds in some topics by some peoples.

I've this script :

 #pragma strict
 
 var mySkin : GUISkin;
 private var toggleGUI : boolean;
 
 
 
  
 function OnGUI () {
 
   
 GUI.skin = mySkin;
  
  
 GUI.Box(Rect(0, 0, Screen.width, Screen.height), "");
  
 if (GUI.Button (Rect (Screen.width/2-950,Screen.height/2-450,70,50), "Skip")) 
  
 {
  
 Application.LoadLevel("Main Menu");
  
     }
 }

But the problem is the timer before showing the button won't work... I want to wait 5 seconds before showing that gui button.

How to proceed ?

Thanks :)