Does New Zealand Hold the Record for Earth's Hottest Day?

No. New Zealand does not hold the record for the hottest temperature ever recorded on Earth.

World Record

56.7 °C (134.1 °F) recorded on 10 July 1913 at Furnace Creek, Death Valley, California, USA (WMO certified).

New Zealand's Extremes

• Highest NZ Temperature: 42.4 °C (108.3 °F) at Rangiora (Canterbury) on 7 February 1973.
• Typical Summer Max: 20–30 °C (68–86 °F).

The "25th" referenced in the query is unclear—it may confuse a date or ranking. Regardless, New Zealand's maritime, temperate climate precludes extremes near the global record.