Final agreement on dealing with Northern Ireland's troubled past, parades and flags must be struck by Monday, the independent chairs of all-party talks has said.
Measures intended to ease months of simmering resentment and violence are extraordinarily close to gaining support, said Dr Richard Haass, adding that the missing ingredient was not more time and urging politicians to grasp the opportunity to do a deal.
A marathon talks session starting at 6am on Monday will bring six months of increasingly intense negotiations to a head after Dr Haass cut short his Christmas break to kick-start one last round of crunch discussions.
He said: "At some point we have got to fish or cut bait, that time has come."
Former US diplomat Dr Haass and Harvard professor Dr Meghan O'Sullivan were asked by Northern Ireland's ministerial executive in July to lead talks after a violent summer of parade and protest.
Serious loyalist rioting broke out a year ago after restrictions were imposed on the flying of the Union flag from Belfast City Hall.
This summer's marching season sparked discord after a decision was taken to re-route a loyal order parade away from a traditional scene of yearly violence in North Belfast.
The talks were intended to provide a framework for when contentious flags can be flown, for dealing with the victims of 30 years of violence which produced more than 3,000 lost lives, and for creating consensus on a new body to decide where members of the loyal orders and republicans can march.
Dr Haass, who gave a press conference before beginning renewed dialogue in Belfast, said an accord was close on parades and dealing with the past but warned cutting a deal on when flags can fly has proven more challenging. He added they were difficult but not intractable problems.
"What we are trying to do is build the peace, to go from ambiguity that may have been constructive once but is no longer, to reach a specificity.
"We belief the draft (agreement) represents constructive specificity."
A total of 24 hours of bilateral and plenary sessions are planned between the parties before a final session starting at 6am on Monday and expected to conclude by the afternoon.
Dr O'Sullivan said there is a need for and a possibility of a meaningful agreement, envisaging that it could set an example and inspire others engaged in peace-making.
"It is not often that you have the chance to help yourselves and help others at the same time. There is an opportunity here worth seizing and it is well within reach."
Dr Haass said Monday was their absolute deadline.
"It will be very hard at that point to argue that the missing ingredient is more time, there has been an enormous amount of time invested."
He added: "We have done this for five to six months, the parties have done this for five to six months. The issues have been worked over from every conceivable angle, a lot of creative ideas have been put on the table.
"We are not going to reach the point where everyone is going to be thrilled with everything... no one is going to get 100 per cent of what he or she wants in these negotiations."
He asked rhetorically: "Would society be better off, both of us believe so.
"We have essentially come to that point, that we have an agreement that is extraordinarily close to a final agreement that would leave both the people as individuals and society as a whole far better off."
The team have refined their proposals into five draft agreements and another is expected before a final deal can be struck.
Dr Haass said he was not prepared to reach separate accords on flags, parades or dealing with the past, insisting that any deal would be a comprehensive one.
"The most progress, frankly, has been reached in the area of the past. Many naysayers said you are not going to get anywhere."
He said it was an error to assume that the negotiations were about producing a lowest common denominator.
"It represents greater specificity, an emergence of new thinking around which consensus can be built.
"I would predict that people will be genuinely impressed, particularly in the area of the past, with both the breadth and depth of content."
He said there had not been the hoped-for consensus on flags but added many of the other core concerns of the parties had been met in ways that are acceptable to others and which advanced the issues.