My guess is: he knew he belonged there, as it was his home; thus opening the door would be perfectly fine; defending his home is his right, thus the shotgun; and opening the door with shotgun in hand would not be risky, 'cause he had the shotgun. His alcohol-laced thinking probably didn't take it much further than that. Any commands barked by the police likely would have floated right by his consciousness, no matter how much time elapsed since he opened the door.
It would be nice if the truth came out and ruled the day, in the trial. May justice be done, whichever way justice requires. Given what we've been told in the official report, it's hard to fault the officers for responding quickly while under the gun.