Portal Settings - Regional Settings - Formats - Date & Time
The format in which a date or a time is displayed in the portal can be defined here. Just click on Date format or Time format in the left area of the dialog.
In the example fields, a preview of the selected format will be shown. The legend in the lower area will inform you of the meanings of the abbreviations used. By clicking Reset format settings all format settings will be reset to the standard settings of the selected location.