I routinely take 5:30-6am flights out of either BWI or PHL. I've also found that there are times when the airports empty and I get through security and others when it seems like everybody's getting to the airport at the same time. I believe it has something to do with the amount of leisure travelers, who tend to get airports earlier, so they may be arriving for a 7-7:30am flight at the same time I getting there for my 6am. Good luck.