[tz] looking for information about changing time zone

Madam, Sir, I’m living in New Caledonia; our local government is thinking about changing time zone (from UTC +11 to UTC +12). Could you please tell me how long a lead notice should be to be sure that the international community will get and process the information ? I understood that the ICAN TZ database is widely used, but I didn’t catch if it is also used for international transports (by airports for example). Could you please tell me if it is the case? If not, whom should I ask for? Best regards, Françoise Kerjouan