...Could be they show up and see you popping off a round in self defense and don't know you are the "good guy"
In this case it wouldn't have mattered. If the guys sitting out frontl of the OP's business had been Goblins all the police would have had to do when they finally did show up would be to take the OP's statement and clean up the mess or worse call the morgue to pickup the OP's dead body and wonder what the heck actually happened.
30 Minutes to respond to a call that there are suspicious characters hanging around outside one's home or business - especially at 2:30 in the morning - is unacceptable unless there's more to this tale than meets the eye.