All U.S.-bound flights departing Abu Dhabi require check-in at least 2 hours in advance. I already had my boarding pass, but I still wound up heading over a couple hours before our rescheduled departure.
An hour and 15 minutes before departure I made my way down to the US preclearance facility. You have to go through security screening again, and then clear U.S. immigration. And you’re required to present yourself at the Customs and Immigration facility no less than 60 minutes prior to flight.