As advised above, your antigen test does not have to be medically observed.
I am booked on a Holland America cruise out of Auckland myself next month and the 'Important Notification' I received last week stated:
"... Guests ages 2 and above are required to take a viral COVID-19 test prior to
embarkation and attest to a negative result. A PCR test may be taken within 48
hours before embarkation or a self-administered Rapid Antigen Test (RAT) may be
taken within 24 hours. Guests who opt for the RAT must take a photo with their
mobile device showing the results along with their full name, date and time of
the test. Please view requirements at https://bit.ly/hal_twfaq "
(bolding of text by me)
No mention of need for medical observation.
In the requirements FAQ mentioned it states:
For cruises visiting Australia that allow an at-home, self-administered Antigen COVID-19 test (RAT), guests should take one photo with their mobile device that meets all of the criteria outlined below:
Negative RAT test next to the guest’s government issued photo ID with a clock showing the time the test was complete (a wristwatch, mobile phone screen or a wall clock, etc.).