What does "incidence of occurrence" mean?

Sorry, but it does basically mean at the moment or time something happens. To adequately answer your question, we need context. Let's say you're looking at your school suspension policy, and the school has a suspension policy for fighting. The student handbook states, "students engaged in fighting on campus will be suspended for 3 days, beginning at the incidence of occurrence." In that context, incidence of occurrence means the suspension begins the day they were fighting. If that doesn't help you, please include the context with your question.