US CBP at YVR is open until 10:30PM --
US Customs and Border Protection YVR
There's a Plaza Premium lounge in the US pre-clearance area that takes Priority Pass --
https://www.prioritypass.com/lounges...usa-departures
Don't know how busy it is at that time, but I'd probably get there 2 - 2.5 hours prior to flight (depending on whether you are checking luggage) if you want to avoid any hassles.