Originally Posted by
bcrdukes
US Customs operating hours at YVR are from 4:30am to 8:30pm. If your flight departs at 6am, best you arrive at 4:30am, but I am only speaking from personal experience as it was complete chaos last time with everyone there waiting for them to be open.
Even then.. they only just start queuing people and letting them in. I'd say they start processing at 5am.
What time to arrive depends on whether you have checked bags, NEXUS/GE, and/or want to eat/coffee before your flight.