Allow for 9am backup
Had a 9am flight to jfk (Sunday), and entered queue for preclearance at t-60, and 30 mins later still only halfway through the line. (I had GE but the baby didn't!)
Luckily at t-20, an AA agent asked for all those on our flight to step out to go through to the front. There were about 15 stuck in the queue.
Silly me, I should have checked the departing flights. Essentially 3 full us-bound planes between 9-930a. This surge of passengers essentially floods the immigration folks. You'd do well to be on the front end of this!