Parses a string that represents an offset in an ISO-8601 time shift extended format, also supporting specifying the number of seconds or not specifying the number of minutes.
Examples of valid strings:
+00:00, an offset of zero;
+05, five hours;
-02, minus two hours;
+03:30, three hours and thirty minutes;
+01:23:45, an hour, 23 minutes, and 45 seconds.