Trigger automation before calendar Event?

So how can I make my home assistant trigger an automation a specific amount of time before an event? Like say I have a doctor appointment at 12:00 noon. And I know i need to be notified 15 minutes in advance of any event because everything I go to normally is no more than 10 minutes away, how do I make it trigger something 15 minutes before the event? Or like maybe 30 idk yet.