Destroy OnGUI ()

How can I get the last button in this code to disappear after say... 5-10 seconds? I tried yield and destroy(this), but they didn't work:

Code (csharp):

1. function OnGUI()
2. {
3.     if (npctrigger)
4.     {
5.     //GUI.BeginGroup (Rect (Screen.width / 2 - 50, Screen.height / 2 - 50, 100, 100));
6.    
7.     if (yesbutton)
8.     {
9.         GUI.Box (Rect(0, 0, 100, 100), "Enter treasure chest");
10.     }
11.     else if (nobutton)
12.     {
13.         GUI.Box (Rect(0, 0, 100, 100), "You cannot enter");
14.     }
15.     else
16.     {
17.         GUI.Box (Rect(0, 0, 100, 100), "Give inventory?");
18.         if (GUI.Button (Rect(25, 25, 50, 30), "Yes"))
19.         {
20.             yesbutton = true;
21.             Debug.Log("True");
22.         }
23.  
24.         if (GUI.Button (Rect(25, 65, 50, 30), "No"))
25.         {
26.             nobutton  = true;
27.             Debug.Log("No");
28.         }
29.     }
30.    
31.     //GUI.EndGroup ();
32.     }
33. }
34.  
35.  

 

Just have a boolean like all your others.. Make it switch after 5 seconds. Put the button into an if{ } block..