Boston's liquor license rules preclude service before 8 am Monday through Saturday and noon on Sunday. One can get a special license for service before noon although that generally is a one-time license. Not sure if DL has a blanket sunday license although I would be surprised. In theory DL probably has to stop serving at 1 am and kick you out at 1:30 (I don't think East Boston has 2 am licenses but I could be wrong). I would pity anyone whose delay had them sitting in the airport that late (although the late AMS flight has been known to leave pretty darn late from time to time).