Tony Blair says government targets have been "too crude" and has promised fewer, more flexible ones in future.
Targets should never become "an end in themselves" or overburden the system, he said in an interview with BBC political editor Andrew Marr.
But they should be kept, along with investment, to ensure improvements are seen in the public services, he added.
It follows claims some GPs are refusing to fix appointments more than 48 hours in advance because of the targets.
The question was raised when all three main party leaders appeared separately on a BBC Question Time Special on Thursday to take audience questions.
Audience member Diana Church said: "You can't make the appointment in a week because you are only allowed to make it 48 hours beforehand."
The Labour leader said he was "astonished", that the logic was absurd and pledged to look into it.
Mr Blair later told the BBC: "In the health service and in schools targets are important, but I think there has been a danger with us, if I am frank about it, that they have been too crude.
"What we need to do is to keep them, but make them sufficiently flexible and not to have so many of them that they overburden the system."
99.9% of patients see a GP within 48 hours, compared to 50% in 1997
2% of GPs' surgeries, according to provisional figures for April, refuse to book appointments more than 48 hours in advance, compared to 12.4% last November
Source: Department of Health
But if targets were axed altogether public services would "start to go backwards", he said.
"The reason that we have got waiting lists so substantially down in the health service, accident and emergency so improved, people able to get to see their GP within 48 hours, is precisely because there has been performance management in the system along with the investment," Mr Blair added.
The surgery concerned says it actually allows patients to book afternoon GP appointments in afternoons, although bookings for morning slots are only taken within the 48 hours.
It says the doctor Mrs Church wanted to see was away on holiday when she wanted the appointment.
Mr Howard returned to his immigration theme
Conservative shadow health secretary Andrew Lansley said targets were causing problems across the NHS, and said a Tory Government would scrap them.
It was an "insult" to doctors for the government to suggest patients would wait longer without targets, he said adding that Mr Blair was "out of touch" with the realities of the NHS.
Lib Dem spokesman Paul Burstow said: "These absurd political targets mean the sickest don't get treated the quickest its time to put patients first."
Dr Hamish Meldrum, the chairman of the British Medical Association's GP committee, also said the targets skewed priorities.
Mr Kennedy highlighted help for the elderly
On the GP targets, he said: "We've always felt that this has been a crude target which has distorted priorities."
On the campaign trail on Friday, Mr Blair again argued the economy was the central issue of the election battle.
He urged voters not to put economic stability and investment in public services at risk by letting the Tories in.
Mr Howard told Question Time he would have invaded Iraq even if he had known Saddam Hussein had no weapons of mass destruction.
Speaking in Cardiff on Friday, he renewed his calls for migration quotas and said his plans to change the asylum system would make it "more humane".
The Lib Dems have focused on their plans for elderly people, including raising the basic state pension for over-75s by £100 a month and free personal care.