I don’t know why the keys creating every 30 minutes. Is it Steamworks limitations or something? Probably 10 minutes will be enough I guess.
As mentioned on the page they want players to enter slowly and not all at once so that it doesnt get too much work fixing everything up.
Keep in mind that these aren’t keys, but is actually just adding the game package to your account.
That does mean it can be removed for any reason at any time.