Few years ago I had 6am flight from mhk, got to the kiosk at 5:31 and they wouldn't let me get a boarding pass (it was 30 min they told me)
Flight was delayed 30 minutes right after that and they still wouldn't let me get my pass. They hadn't even opened up security yet.
I was pretty bummed and then had to pay $75 or something to change to the afternoon flight.