AA sent me a notification to check in for my flight, - which was kind of wonky anyway because it only indicated the DCA-CLT segment instead of all the way through to PLS - but when I tried wasn't able to. Said must be done in person tomorrow. Assume this is because I have to show my entry approval letter from PLS? There appears to be no mechanism to upload.

AA's portal advises check-in 3 hours prior for international flights. I'm checking a bag so planned on being there 2 hours prior, with all relevant documents printed and available. My flight is at 640am tomorrow morning. I'm flying in J so will be able to use the priority line (assuming it's open).

Is three hours really necessary? (Will the check-in counter and security even be manned at 3:40am at DCA?)

Obviously I don't mind if that is truly necessary, but I'd much prefer not to be hanging out in the airport, even masked, for any more time than reasonably needs to be allocated.