So I can comment about this, as I had a neighbor run a generator in their yard for over a week after they failed to pay the electrical bill.

You are pretty much SOL during daylight hours, unfortunately. The only time the after hours effect comes into play is after 10 PM, and at that point the police have to measure the sound from a specific distance from your house with a calibrated instrument.

So unless they run them after 10PM, there's not much you can do from any authorities.