User day and night locations are kept very securely on Swiss servers.
If you have added an email address in the Settings page, this is associated with your unique data, so that your tracked days and nights can be recovered at a later date if necessary.
Only the day and night country location is stored and no detailed local positioning information is collected, this is only viewable by you from within the App.
If you prefer even more privacy, you can select 'Partial Tracking' in the Settings page. Then only the country location will be stored on your phone and no local movements are stored or viewable.