The earliest the better, be there by 4 or 4:30am give yourself enough time to check in and go through airport security..
I'd try to be there at 5:30 to be careful, but my relatives usually do well even later.
Are you TSA-pre, and are you checking luggage?
One item a small fraction of the population forgets is to check into your flight 24 hour prior. Check-in usually is cut off 30 minutes prior...but certain Airlines cut off is 40 minutes prior. Another forgotten item is that the doors to the flight closes 10 minutes prior and they can actually leave a few minutes earlier than that if the pilot in command/airlines call times up. Bottom line if you need to visit the airline counter for any reason (check a bag, need gate assistance, unaccompanied minors flying, International travel, etc)....get there 2 hours prior.
Airlines counters open at 4am typically, make time for extra searches in case that happens. I would arrive no later than an hour beforehand.
No later than 1 hour before you plane is scheduled to leave.
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