Guess everyone is different. When I sleep on the plane I don't want to wake up in a few hours for landing, sit around for one hour doing nothing, and go through the take-off drill again. If JFK-YVR-HKG say departs at around 6-9 p.m. it would be an excellent flight as you don't need to sleep or doze off on the first part. However, by being a late departure when people are tire and generally falls to sleep right away, having to wake up again is a huge pain in the butt.