If your flight is at 6:20am, doubt immigration will be open two hours prior - in fact, YVR website states it only opens at 4:30am.
Haven't been through YVR pre-clearance there in a while, but at peak times, if you don't have Nexus/GE, YYZ T1 can be 1 hour wait, and at real peak, they can even meter people into the custom hall, based on flight time (though haven't heard of that happening in a while). I've also seen several people re-booking at the AC desk post-immigration Sunday evening because they didn't clear in time to make their flights. And IME, while they used to do it years ago, they do not allow people to go to the front of the line if their flight is close - I have mixed feelings about this; I have used this in the past (long time ago) when I was arriving late from a connection, but that process is separate now, but it also invites the gamers to show up late and take advantage.
No matter what, check-in will close at 60 minutes prior to departure, and bag tags will need to be printed by then (and I don't think there's any leaway with that ex-Canada). But if you don't have Nexus/GE, I'd arrive at least 90 minutes prior to departure, maybe a bit earlier. With trusted traveler status, 60 minutes should be sufficient, but again, give time to get through the check in line if you haven't printed a boarding pass from OLCI.