The correct time to ask for the permission is when the user attempts to set up geofencing, at which point the phone OS should present a geofence picker that sto

The correct time to ask for the permission is when the user attempts to set up geofencing, at which point the phone OS should present a geofence picker that stores the fence in the OS and notified the app on entry/exit. The app itself has no need to know what the geofence coordinates and radius are, so by implementing the geofence at the OS level you can optionally as app author decline to care what its coordinates are — and thus have no need to request location access at all.