I've done several 6am flights to the US thru YVR. I'm the type who prefers to get to the airport early. a) So I never have to worry about getting caught in a line and rushing to my gate. b) I really enjoy relaxing at the airport people watching
That being said after a couple of 'Hurry up and get there just to wait' I now aim for 4:30 arrival (not later) at YVR for 6am flight and usually I am airside by 4:45.