Even by the standards of UN climate meetings, with their jargon, rhetoric and countless committees, when a whole conference overruns by 36 hours something must be up.
Environment ministers tried to sweep aside a 16-year-old divide between industrialised and developing countries at a meeting in Durban, South Africa, which finally wrapped up at 5.00 a.m. on Sunday.
In the end, they may have fallen narrowly short: the proof will be in the deal they agree in 2015.
After several sleepless nights negotiators were desperate to conclude and objections from India resulted in a watered down text which left the door open to future wrangling.
In 1995 in Berlin, countries unambiguously launched negotiations on a legally binding protocol, which they agreed would only require emissions cuts by the world's industrialised economies.
The United States refused to ratify the resulting Kyoto Protocol, arguing that it unfairly excused China.
On Sunday, emerging economies including China, which is now the world's top carbon emitter, appeared to accept an equal legal commitment to fight climate change alongside the United States (Kyoto backers already face binding emissions caps).
This was significant: China agreed to move in step with Washington, even though the United States is still a far richer country, has cumulatively pumped out more greenhouse gases and arguably has made no more effort than China since 1995.
Durban was also important because by launching negotiations on a global climate deal - to come into force after 2020 - the conference met a condition set by a handful of Kyoto backers to continue their binding targets under the protocol.
But there's trouble ahead.
First, the rest of the world will now lean on voluntary national climate pledges for the rest of the decade.
Both these pledges and the continuing, Kyoto commitments are widely recognised as inadequate collectively to stave off dangerous climate change.
Second, negotiations meant to conclude in 2015 will be over-shadowed almost immediately by elections next year in the United States, where some Republican contenders doubt humans are causing climate change.
The hope of more convinced politicians is that the financial downturn will blow over and growing evidence of climate changes will harden public demand for action.
Third, the wording to agree a new global deal does not unambiguously commit all countries to a binding protocol.
The Durban text launches negotiations on "a protocol, another legal instrument or an agreed outcome with legal force".
These words differ slightly with the Berlin meeting which launched negotiations on - "a protocol or another legal instrument" in 1995, ultimately agreeing Kyoto.
It's quickly apparent that the Durban text has added something - a potentially fateful fudge.
Some reluctant countries may argue that "an agreed outcome with legal force" could include merely voluntary pledges confirmed at a U.N. conference.
Even if the text proves robust, there is much to discuss including the level of ambition of future carbon emissions targets, which countries they should apply to and what sanctions should be imposed for non-compliance.
Encouraging in Durban was a new coalition of European and poor developing countries that may gather too much force for emerging economies and the United States to ignore.
Only if the world agrees a full protocol like Kyoto will they reap its advantages, compared with a tamer system of domestic pledges.
It's become fashionable to argue against a politically difficult internationally binding deal. But a protocol like Kyoto defines common rules, forces compliance, makes countries plan beyond election cycles and creates a clearer picture of collective action.
Kyoto is a rule book which established mandatory climate action, carbon trading, climate accounting and sanctions.
It would be unfair to judge Durban solely by a few ambiguous words.
In other, limited success, the conference launched a Green Climate Fund meant to channel billions of dollars to developing countries, while environment ministers from more than 100 countries promised to work to engage the private sector to help finance forest protection and other climate action.
It also committed countries to count their greenhouse gas emissions and report back every second year on steps taken against their voluntary pledges, while the U.N.'s climate secretariat would compile a review of progress made.
The failure of all such conferences has been on ambition.
Countries committed under the 1992 climate convention to avert dangerous climate change.
Four years ago a U.N. panel of climate scientists, in its Nobel prize-winning review, said for the first time that global warming was "unequivocal" and that global greenhouse gas emissions should stop rising by 2015 to limit warming to what are generally considered safer levels.
Carbon emissions from burning fossil fuels this year will rise at exactly the same rate (3 percent) as the annual average over the past three decades.
In Durban, the United States applauded voluntary pledges through 2020 which are well-known to be inadequate.
At a fork in the road between voluntary or legally binding action, Durban's greatest success was to push negotiations down a legal route, in a victory for multilateral rules-based action.
(Reporting by Gerard Wynn; Editing by Anthony Barker)