We had a connecting flight from West Palm Beach to Manchester at BWI. We started the line one and a half hours before departure time.
So, I would guess that you should arrive at the airport at least 2 hours in advance because if BWI is your originating airport, you would have to check in and it is likely that you will go through 2 security checks before even getting in line to obtain a boarding pass. It just a "have patience and allow time" issue really. Have fun!! : )