Following all the advice on FT, I went to preclearance late, about 1 hr before the scheduled departure time of my flight to Chicago. This is the last of the middle-of-the-night departures. The listed boarding time was 1.5 hrs before the flight, and the premium lounge had completely emptied out except for a few people sleeping on the sofas with their shoes on. Floor and table cleaning was in full swing, so finally I chickened out and left the lounge.
At that point the corridors towards preclearance were deserted, security was deserted (except for staff), the preclearance area was deserted (except for staff). The friendly immigration officer waved me through without showing me images of my bags. Me: "No photos to see?" Officer: "No, not necessary." Me: "Is that because mine are the last two bags left?" Officer: "That's right, they've got to be yours." In all about 5 min.
Of course, the post-pre-clearance lounge was packed to the gills.