GUI Label disappear???

Hey, I am working on a game like Submachine just 1st person. If you don't know what Submachine is just google: Play Submachine 1 Online. Because Submachine 1 is the best :) Now, I created a door and If you don't have the key It shows a GUI label, you know I did like this:

function OnGUI() { if(inZone == true) { if(noKey == true) { GUI.Label(Rect(10, 10, 150, 150), "You do not have the key for this door!"); } }

Well, this is probably very confusing because all of the variables are not shown right there, but what ever... How can I make the text disappear after a limited time?