The doomsday 7 p.m. ET deadline for Nancy Guthrie’s family to cough up $6 million to the villains who claim to be holding her came and went Monday — as TV star daughter Savannah issued a desperate new plea for help.

“We are at an hour of desperation,” the “Today” show star said in an Instagram video Monday afternoon — just three hours before the deadline that her 84-year-old mother Nancy’s purported kidnappers set in a ransom note after she vanished from her Arizona home more than a week ago.

The daunting deadline passed with no sign of the ransom being paid or proof that the ailing grandmother was still alive — leaving her fate in question.

The bitcoin account given by kidnappers showed zero balance and zero transactions.

The supposed kidnappers had claimed Nancy would be in danger if they didn’t get paid by the deadline.

The FBI and Pima County Sheriff’s Department still haven’t verified whether the ransom note is authentic or the work of scammers, but with no other known leads to go on, Guthrie’s family and the cops have treated it as the real deal.

However, former FBI agents have increasingly expressed skepticism about the authenticity of the ransom demand — which referenced Nancy’s Apple Watch and a floodlight at her home.

“I’m very skeptical of this,” former FBI Assistant Director Chris Swecker told Fox News’ “The Big Weekend Show” on Sunday.

He added: “If this was a kidnapping, it would be a very simple matter to authenticate and provide proof of life.

“You have to allow for the possibility that this was something more or something other than a kidnapping.”

Follow The Post’s live updates on Savannah Guthrie’s missing mom

Savannah and her siblings, Annie and Camron, even put out a video Saturday telling the alleged abductors that they were ready to pay.

The latest video Monday revealed the desperation that’s been mounting as Nancy — who has major heart and walking issues — remained missing for a ninth day.

“We believe our mom is still out there,” Savannah said. “She was taken, and we don’t know where.

“I’m coming on just to ask you not just for your prayers, but no matter where you are — even if you’re far from Tucson — if you see anything, if you hear anything, if there’s anything at all that seems strange to you, that you report to law enforcement,” she said.

“We need your help,” she added.

Nancy hasn’t been seen since Jan. 31 when her son-in-law, Tommaso Cioni, dropped her off at her Tucson home after she had dinner with him and Annie.

She was reported missing the next day when she didn’t show up for Sunday church, and police soon ruled the search a criminal investigation after they found signs of a struggle at her home.

Matching ransom notes showed up at three news outlets Monday and Tuesday and set two deadlines for different demands — $4 million paid in bitcoin by 7 p.m. ET last Thursday, or $6 million to be paid by 5 p.m. Arizona time (7 p.m. ET) Monday.

The note provided no proof of life or images of Nancy but described details about the crime scene in an apparent attempt to corroborate its veracity.

And it claimed Nancy would be in danger if the Monday deadline passed without payment.

The supposed kidnappers then went quiet — until Friday, when a second message was purportedly sent.

That letter’s exact contents remain unclear, but it included a description of Nancy while reiterating that she could be harmed if Monday’s deadline passed without payment, NBC News reported.

Police likely spent the last hours before Monday’s deadline passed frantically going over their work so far in an attempt to find any leads that might break the case and save Nancy, law enforcement experts told The Post.

“They will be going back over a lot of their previous leads again, interviewing individuals again, checking all the cameras that we have on buildings, intersections, things like that,” said former SWAT Cmdr. Bob KrygierI, who used to work with the Pima County Sheriff’s Department, which is leading the search for Nancy.

“I guarantee they’re following up on every lead they’re given,” Krygierl said.