No matter what you do, there is always someone that is going to complain. Even if you notified the neighbors ahead of time that you were going to fire at 1600 hrs. Some people just aren't happy regardless of what you do,
This, this a thousand times this! I learned a long time ago that there's a certain percentage of the population that literally aren't happy unless they're mad about something. If there's nothing to be mad about? They'll invent something.
If I'm in conflict with someone, I'll bend pretty far to accommodate a mutually agreeable compromise. When I recognize they're just one of those "bless your heart" people, my offers come off the table and I walk away. Nothing is more frustrating than trying to appease and unappeasable person.
That being said, I agree that perhaps a note to the neighbors offering to let them see your safety precautions might put some of them at ease and make for better relations. If not, nothing is lost in the effort!