If you have not had your docs checked by T-60, I would expect to be removed from the flight. To assume anything else would be irresponsible. As far as when to arrive to ensure you accomplish this by T-60, that's up to your comfort level and knowledge of your local airport. At my local airport, I would probably aim to be walking in the door of the terminal around T-75 (a 15 minute buffer) but at some airports that would be a disaster!