This method is approximately equivalent to calling GetSystemDefault()()()() with an implementation that wraps BclDateTimeZoneSource (e.g. Bcl), with the exception that it will succeed even if the current local time zone was not one of the set of system time zones captured when the source was created (which, while highly unlikely, might occur either because the local time zone is not a system time zone, or because the system time zones have themselves changed).

This method will retain a reference to the returned BclDateTimeZone, and will attempt to return it if called repeatedly (assuming that the local time zone has not changed) rather than creating a new instance, though this behaviour is not guaranteed.