I think my record was getting to the airport two hours ahead and into a line of about 25 people at T-90 minutes, and reaching the desk at exactly the scheduled departure time! (This was YWG on the last day of the Pan American Games, so many passengers spoke no English or French, and also did not seem to understand that you can't carry five large suitcases onto the plane.) And there were quite a few people behind me too... with the next departure for ORD scheduled 11 hours later, they quite sensibly held the flight.