At most, Cunliffe had just 14 months to reconnect Labour with the voters who had turned their backs on the party at the 2008 election and who subsequently seemed not to have the slightest interest in listening to what Shearer or his predecessor, Phil Goff, had to say or offer.
Cunliffe - who has probably lost another month, given the election is likely to be in October rather than the traditional Saturday in late November - seemed well aware of the ultra-tight timetable with which he was working.
He immediately announced his MPs had been placed on a "war footing". But they have yet to leave the barracks.
The opinion polls since have offered little succour. The party's rating at just under 32 per cent in the latest Fairfax survey, which indicated National might be able to rule alone, is said to have had a chilling impact on the Labour caucus.
The continuing high levels of support for National are making a nonsense of the two absolutely essential tasks required of Cunliffe.
First, he has to build a mood for a change of Government when there is no sign of any such feeling abroad in the wider New Zealand electorate.
Second, Cunliffe has to persuade voters that Labour is the party that must be given a strong mandate to carry out change.
That would normally call for fresh ideas to excite voters. The problem for Labour is that the voters do not want to be excited and are happy with what is dubbed the "progressive conservatism" that is the hallmark of John Key.
As it is, Cunliffe has precious little to show from his five months in the job. A peaceful Labour Party conference and a comprehensive byelection victory in a safe Labour seat do not really count for much.
When it comes to fresh policy that was not in the last manifesto, there is Shearer's promise to build 100,000 affordable homes over 10 years.
National is fighting back strongly on that front and its solutions are rooted in the here and now and are now yielding results, whereas Labour has yet to provide the full detail of how its policy will work.
There is Shearer's promised revamp of the wholesale electricity market and the claim it will mean lower power prices. But power consumers struggle to follow the complex debate and anyway have been promised much before only to find themselves paying even more.
Then there is the new publicly owned insurance company, KiwiAssure. And, of course, there is the $60-a-week "baby bonus".
The latter policy is the clearest indicator yet of the direction in which Cunliffe is taking Labour.
It was the result of a considerable amount of work, much of it done by Jacinda Ardern, the party's spokeswoman on children.
The policy is bold in applying to most children aged between zero and three years - a crucial time in a child's development, but one from which the state is comparatively absent.
The policy also marks a return to near universality in the wide scope of the payment. It flags the seriousness of Cunliffe's Ed Miliband-like talk of Labour's policies being all about "fairness and opportunity".
The baby bonus was well received by voluntary organisations working in the social sector.
The challenge for Cunliffe is to explain how such policies interact with things such as Labour's promotion of a capital gains tax.
The bigger picture is lacking. There is also a lack of urgency, which is failing to provide the momentum to keep Labour in the headlines for the right reasons - rather than trying to ping John Key for living in a "leafy suburb" when you do likewise.
Cunliffe has also been unlucky in losing his office chief of staff - an absolutely pivotal position.
But, according to one expert, Cunliffe's looming problems are not solely his fault.
They say it takes one to know one. And Bill English sure knows better than anyone else exactly how it feels to be David Cunliffe right now.
Although English's voice was its usual mixture of dry humour and sarcasm, it had the occasional tinge of sympathy as the Minister of Finance spoke in Parliament on Wednesday afternoon, doing what he loves doing - dissecting the Labour Party, diagnosing its various ailments and predicting it will fail to overcome them before voters roll up to the polling booths.
English blamed "lazy and weak" Labour MPs for failing to take the pressure off their leader. He said Shane Jones gaining headlines with regard to his allegations against Countdown had only served to show up the poor performances of his colleagues.
It is something English understands full well. It was from the same uncomfortable but potentially rewarding position that Cunliffe now occupies - Leader of the Opposition - that English led National in 2002 to its worst defeat in the party's history.
