Calling the cops is the last resort, not the first. Neighborhood watch can solve this. And spank some kids.
Most states and jurisdictions have laws that one way or another address TERRORISTIC THREATS.
Call your police, sheriff, State Police, FBI, ATF, and Homeland Security and report these time delayed bombs. Your street will have numerous telephone trucks parked at the curb during the times that this monkey business happens. They will be caught and taken to the board room, and someone is going to be fired.
Ideally, you'd love to be able to convince them that you've served a lengthy prison term for manslaughter, and that rumor has it you keep severed human heads in your freezer. That isn't always easy, though -- and may result in some permanent damage to one's reputation. LOL.