A decision on whether National or Labour will lead the next government could be announced after a meeting of NZ First's board and caucus on Monday.
Party leader Winston Peters can't guarantee the timing of an announcement and board members are booked for an overnight stay in Wellington if necessary, but he says "time is of the essence".
The board has 14 members, including Mr Peters and his deputy Ron Mark.
The party's other seven MPs will take part in the meeting.
NZ First's caucus has been meeting since Thursday night, when coalition talks with National and Labour ended.
The MPs are drafting option papers for the board meeting which set out the details of the deals on offer from the main parties.
They're also working on the advantages and disadvantages of the different types of government NZ First could go into.
The options include a majority coalition with cabinet positions or a support agreement such as ACT, United Future and the Maori Party had with the 2014 minority government.
There could still be contact between NZ First, National and Labour over the weekend although the formal talks have ended.
The option papers have to be checked with the main parties to make sure they're accurate, and both sides know exactly what they're committing to.
"Any communication now will be between key officers and key operatives on either side so we can sort it out by phone call and text communication," Mr Peters said.
Comprehensive dossiers were built up during the negotiations.
They contain details of the concessions offered by National and Labour that will allow NZ First policies to be implemented by the next government.
There's nothing in them about ministerial positions - Mr Peters says that's something that can be worked out later.
The Greens are essential to a centre-left government because Labour and NZ First don't have enough seats between them for a majority, but they've played no part in the negotiations.
Mr Peters insisted on negotiating only with National and Labour, leaving it up to Labour to deliver the Greens' support.
If NZ First backs Labour, the Greens will have to ratify their part of the agreement by holding a special meeting of about 150 delegates.