The court was told the US had to make a formal request to New Zealand's Ministry of Justice within 45 days to surrender McKelvy.
Under Article XI of the bilateral extradition treaty, if the extradition request is not filed within that timeframe, the person must be set free.
The deadline for the US to make the request is January 2.
The court heard the request for McKelvy's surrender would be submitted through diplomatic channels imminently, probably tomorrow.
That request could then be filed in the District Court next week.
The request alone does not make extradition inevitable, as New Zealand courts must consider what happens next.
McKelvy appeared by audiovisual link from a small booth in jail wearing a green prison-issue jersey.
He shared a laugh with others in the courtroom when Judge Fraser voiced relief that the audiovisual equipment was working, after an earlier defendant was muted.
He was remanded in custody until his next hearing on January 20.
McKelvy's notoriety emerged from his role in scams including a sophisticated mortgage racket in the early 2000s.
That conspiracy included a Who's Who of dodgy lawyers, accountants and property valuers and swindled $6.4million from victims, including the unwell and the elderly.
The DEA has also indicated interest in New Zealanders Marc Patrick Johnson and Michael Murray Matthews.
Johnson and Matthews were arrested on cocaine trafficking charges in Romania last month.