Lawyers for the man convicted of killing six-year-old Etan Patz asked a judge to set a tight deadline to determine his fate, after an appeals court ordered a new trial or release.

In July, an appeals court cited issues with Pedro Hernandez' police interrogation, his history of mental illness and the jury instructions at trial as reasons to reconsider his 2017 conviction.

On Thursday, Manhattan prosecutors - trying to preserve the conviction - asked for 90 days to make a decision on retrying Hernandez. The defence pushed for a decision in 30 days instead.

US District Judge Colleen McMahon said she would rule in a few days, noting it has been decades since the "nightmare" of Etan's disappearance.

The May 1979 disappearance of Etan Patz while he was on his way to school in New York City brought nationwide attention to missing children.