He added: "We have invested appropriately in the homework beforehand ... and now we need to do the business in the time available."
Mr McCully said the decision by the Commission for the Conservation of Antarctic Marine Living Resources to call a special meeting for the first time in its history to discuss the MPA showed how seriously the members were taking the proposal.
It was called after members failed to reach a consensus in Hobart in October, to the exasperation of some countries and conservation groups.
If they failed again, members could make another attempt at future meetings. But New Zealand felt this was the best chance to get approval for the proposal, and any further delays increased the risk of failure.
The CCAMLR negotiations took place behind closed doors, but official documents showed that Ukrainian and Russian delegations doubted the scientific merit of an MPA and were concerned about the interference with their fishing interests.
China, Japan and South Korea also held some reservations.
It is understood that despite intense lobbying in the past eight months, Ukraine and Russia were still not convinced of the merits of the proposal.
Asked how nations with fishing interests could be persuaded to back the MPA, Mr McCully said they needed to understand that it was in their long-term interests to have scientifically backed management of the Ross Sea.
Counting the votes
Where do member countries stand on a NZ-US proposal for a Ross Sea marine reserve?
United States: The reserve is "based on an exceptionally strong foundation of Antarctic science built by ... scientists over the past half century".
Australia: The Ross Sea proposal has "a very strong scientific foundation".
European Union: "These proposals are based on the best available science and require no further scientific discussion."
Ukraine*: "If we want to introduce this conservation measure, then well-grounded scientific arguments need to be put forward ... Unfortunately, they are lacking here."
South Korea*: "The Korean delegation expresses its strong support for the establishment of the MPAs".
Chile*: "Chile favours and promotes ... the establishment of MPAs supported by clear scientific evidence."
Brazil: "Brazil sees important merits in [the] MPA proposals."
Argentina*: "Argentina reiterates its strong commitment to reach a positive outcome ... with regard to MPAs."
Other countries:
Belgium, France, Germany, India, Italy, Japan, Namibia, New Zealand*, Norway*, Poland, Russia*, South Africa*, Spain*, United Kingdom*, Uruguay*.
*countries with fishing interests