England's qualifications watchdog has said five new vocational diplomas could be introduced by 2008, one more than the government has promised.
Significant changes to the exam system are planned
The Qualifications and Curriculum Authority had said the timetable would cause a "tension" with the need to try out the proposed changes properly.
But after consulting skills experts it now believes five will be manageable.
Previous problems with exams have been attributed to rushed implementation.
Concerns by the authority (QCA) were raised at its board meeting in March, newly-published minutes reveal.
Officials gave a presentation summarising the key issues in the government's reform plans for 14 to 19 learning in England.
Those plans were its response to the Tomlinson report it had commissioned, which had recommended diplomas to cover all existing academic and vocational qualifications.
The QCA had said it was important to implement Tomlinson in full.
But the government said GCSEs and A-levels would stay, and it would introduce diplomas in vocational subjects.
Its white paper said: "The first four diplomas in information and communication technology, engineering, health and social care and creative and media will be available in 2008. Eight will be available by 2010."
Another presentation to the QCA board looked at the timeline for implementing the things it would have to do as a result.
"There is a tension between trialling proposed changes properly and the need to have them in place by a certain date," the minutes said.
"There is a possibility that QCA will advise against rolling out four live diplomas as early as 2008."
Some board members expressed concern about the timescales involved.
It agreed to itemise the risks associated with the programme.
The Department for Education and Skills (DfES) observer at the meeting, Peter Housden, is recorded as agreeing that "the balance between quality of change and speed of delivery is very important".
The concerns were reinforced at the next meeting, in May.
There was a warning that schools and colleges needed to be considered, "as a potential clustering of new initiatives in 2008 will have a significant impact on staff workload".
But a spokesman for the QCA said on Friday that it now believed five diplomas could be introduced in 2008 - the extra one being "construction and the built environment".
He said the change of heart followed discussions with those who would be involved, including sector skills councils.
Concerns about the need to pilot the new qualifications and not to rush still applied, he added.
The DfES said it was "committed to making rapid progress, but not at the expense of the stability of the system - QCA and DfES working together on a timescale that strikes appropriate balance".
The general secretary of the Secondary Heads Association, John Dunford, said things must not be rushed.
One of the great benefits of the Tomlinson recommendations had been the long lead time - 10 years - "probably the first time we have had a sensible timescale".
"I would caution against haste for the sake of it."
He said his members were already flagging up concerns about workload.
"The QCA is right to be aware of the danger of too many curriculum changes at the same time.
"We have had that before and it was a disaster," he said.
There were widespread complaints that the changes to A-levels five years ago, with the introduction of AS-levels and A2s, were rushed.
The then education secretary, Estelle Morris, said after ordering an inquiry: "They weren't the best implemented set of curriculum reforms that have ever happened."
She told MPs in 2001: "The way the AS-levels reforms were introduced last year did not do credit to anybody who had responsibility for the implementation."