Is it incumbent upon a Muslim in New Zealand, where the day first dawns, to follow the timing of Islamic countries for the commencement of the Ramadan fast, or to follow what local Muslim leaders decide, knowing that their decisions may be incorrect?

If the Muslims in your country sight the crescent moon with a legitimate sighting, then the fatwa is that each country's inhabitants have their own sighting, and this is the new view of the Shafi'i school. However, if people do not rely on a legitimate sighting but rather on astronomical calculations, then the beginning or end of the month is not established by them according to the general body of scholars. In this case, you must complete Sha'ban as thirty days if you do not sight the crescent moon of Ramadan. It is permissible to act upon the sighting of another Muslim country that shares a part of the night with you, based on the opinion that sighting in one country is a sighting for all other countries.