Talks aimed at restoring devolution are expected to continue today but the prospects of agreement last night looked slender.
Despite the two goverments' relatively upbeat mood in the morning, the atmosphere later in the day appeared to have soured with legacy issues proving a stumbling block.
Sinn Féin accused Secretary of State James Brokenshire of blocking access to justice for families who have waited decades.
Newry and Armagh MLA Conor Murphy said the British government was "kicking this can down the road forever".
"There are families out there waiting 45 years for access to justice," he said after emerging from the discussions yesterday evening.
"The British government cannot continue to deny them access to justice."
Mr Murphy said the negotiations were entering a critical time.
The assembly will meet on Monday and, following the March 2 election, must nominate a first and deputy first minister.
If the key executive posts remained unfilled at 4 pm then legislation dictates that the secretary of state must call an election within a 'reasonable time'.
Sinn Féin has insisted that it will not support DUP leader Arlene Foster's nomination as first minister.
The Ulster Unionists also sounded a pessimistic note, warning there was limited potential for a deal to be struck in time.
UUP chief negotiator Tom Elliott said: "Whether we can make the deadline is still questionable.
"We have no idea how long the talks will go on for or if they will go beyond that 4pm Monday deadline."
However, Mr Brokenshire said discussions had been constructive.
"There are a number of issues where I see common ground and where I firmly believe that resolution can be achieved," he said.
Foreign Affairs Minister Charlie Flanagan said it was important agreement was reached on Monday.
"Often minds are focused intensively once clocks are ticking loudly and once deadlines are looming.
"We are now entering that phase."
In the wake of Martin McGuinness's funeral on Thursday, where Mrs Foster received a spontaneous round of applause, it had been speculated that there was a greater desire to reconcile differences and strike an agreement.
By yesterday evening, however, much of that optimism appeared to have evaporated.
Speaking yesterday morning Mr Brokenshire had signalled that a deal was achievable "with good will, good spirit and that positive intent."
"But time is short and we must firmly focus on those key issues to enable an executive to be formed on Monday," he said.
