What is disturbing the peace?

my neighborly neighbors dirtbike all day and night around their house and i have never said anything trying to be neighborly ( we can't even have a conversation its so loud in our back yard and all we smell is gas) but now that they have called the police on us because my son through a water balloon at his car i would like to know. at what time are they supposed to stop and even if it is before this time if it bothers us what can we do.