If your travel time to a physical place is a key factor for your events, Calendar for iOS can now alert you based on how much time you need to travel from your current location.
In order to trigger this option in the Alerts section of a new event, you need to add location to the event near the top, just below the event name. When you search for a location, make sure it has a red pin; that means Calendar pulled an actual location from Apple Maps. If the pin is gray, it means Calendar and Maps couldn’t find a physical space, and they’re just accepting whatever you typed as a place-less name.
Once you add a location to your event, the Alerts option will show “Time to Leave” as an option. iOS will now use your location, the event’s location, and current traffic conditions to determine when to bug you to get going.
A drawback of this option, however, is that it’s hardwired to use driving directions. If you use transit or walk to your events, this option might be a little less useful.