"The ministry [Culture and Heritage] intends to complete the project well before the 2027 deadline," Te Pae Mahara manager Brodie Stubbs said.
The ministry refused an interview and issued a statement.
RNZ asked the council to explain the rationale for extending the deadline by five years.
"The reason it's got the extension is because it's a Category One heritage building, it's empty and it's in a relatively isolated spot so the risk it poses to the public is relatively low," council spokesman Richard MacLean said.
The ministry has told the Royal New Zealand Returned and Services' Association (RSA) its "ideal completion date" is before Anzac Day 2023 - but told RNZ this is for "planning purposes" rather than a confirmed date.
"The ministry is still working through planning to confirm an official date of completion," it said.
Not only the tower, but the Hall of Memories adjoining it cannot be accessed.
The Carillon is in one of the riskiest categories of buildings.
The ministry thought it had nailed the restoration back in May 2018, when its chief executive announced the reopening of the restored belltower, saying: "It's been a long process, involving a dedicated team of experts overseeing this remarkably detailed operation, and thanks to them we can now celebrate the bells' return."
The council celebrated by noting in its public notices: "Restored Carillon sound as a bell."
The first warnings the bells were at risk of falling on people had come in 2011 from an engineer (some insiders still dispute that this is a real risk). The bell frames were severely corroded.
However, only a partial cut-price restoration was done, and in 2020 it was revealed the frames were still too weak - as, it was later revealed, was the tower structure itself.
The ministry said it recently outlined its new strengthening plans to the council.
"The project will see one of New Zealand's significant heritage sites re-opened to the public and restored to its full ceremonial and commemorative purpose," said Stubbs.
MacLean said the Carillon stood in a park that was not used much, which factored into its risk profile.
He denied the ministry's failure to get the job done sooner had forced the council to extend the time.
"I don't think anyone's being forced," he said.
"They've obviously got some challenges partly because of the heavy bells at the top, but also the shape and height of the structure.
"Whether we would prefer that the building was up to code now, of course we would, but we have to be realistic about this as well."
The RSA was approached for comment.
During strengthening, Pukeahu National War Memorial Park will remain open, and commemorations continue to take place at the Tomb of the Unknown Warrior.
The Queen Elizabeth II Education Centre at Pukeahu remains open for school visits.
