How to prevent notification showing up when an event in my calendar is occurring?
Their is a notification program in android already if you are on Android 4.4+ 

4.4+ ... Hold on the notification and go to app info, Then deselect show notifications

5.0+... Hold on the notification and select hide notifications from this app or notifications like this !

Then manually turn the apps back on again !

The notification manager is in different sections of the settings for each device.. Some it is under display and others it's under privacy (sms reasons)