A common myth that goes about from time to time is that Queen’s Birthday weekend (now King’s birthday weekend - more below) will be abolished automatically once we become a republic. This isn’t the case.

Public holidays in New Zealand are defined by section 44 of the Holidays Act 2003:

The following days are public holidays:
(a) Christmas Day:
(b) Boxing Day:
(c) New Year’s Day:
(d) 2 January:
(e) Waitangi Day:
(f) Good Friday:
(g) Easter Monday:
(h) ANZAC Day:
(i) the birthday of the reigning Sovereign (observed on the first Monday in June):
(ia) the day on which a public holiday is observed to acknowledge Matariki (Te Rā Aro ki a Matariki/Matariki Observance Day) (see Schedule 1 of Te Ture mō te Hararei Tūmatanui o te Kāhui o Matariki 2022/the Te Kāhui o Matariki Public Holiday Act 2022):
(j) Labour Day (being the fourth Monday in October):
(k) the day of the anniversary of a province or the day locally observed as that day.

The reigning Sovereign’s birthday (subsection (i) above) is simply defined on the first Monday in June. This is why there isn’t an amendment required to rename the holiday from Queen’s to King’s birthday weekend.

On becoming a republic, nothing about this section would change - a deeming provision making all references to “Sovereign” in our law be read as “Head of State” would not make any difference, as the day is defined as the first Monday in June.

Of course, we’d prefer to have a new date for this holiday, something actually relevant to Aotearoa. There’s a number of candidates, but given the spacing of the holidays (King’s Birthday and Matariki now occur about the same time), it would make sense to hold the public holiday marking the creation of a New Zealand head of state sometime in September.