The appeal for a new £9m cafe at the top of Snowdon faces a shortfall of £1.4m, the Snowdonia Park Authority has been told.
The appeal stays open until 'all funding opportunities have been explored'
This Friday's deadline has now been extended indefinitely.
The closing date to raise the remaining sum was first set for June but was put back due to lack of support.
But park authority chief executive Aneurin Phillips said he had been "encouraged" by support from key interests.
Earlier this week, a report to the autthority, leaked to BBC Wales, claimed a bid for a £750,000 Heritage Lottery Fund grant had not materialised.
It claimed that the appeal "continues to attract a trickle of funds but despite further direct approaches to potential funders, no new major sponsors have come forward".
About 350,000 people visit Snowdon each year, but its 70-year-old summit cafe is seen as outdated, and was once called "the highest slum in Wales" by Prince Charles.
During Wednesday's meeting Mr Phillips said: "This is an ambitious project for such a small authority and we have been encouraged by the support we have received from key interests, including the Welsh Assembly Government, Wales European Funding Office and other interests such as the Snowdonia Society".
The concrete cafe dates from 1936
The replacement building for the current cafe would also include a visitor centre and new Snowdon Mountain Railway terminus.
The park authority said talks had been held with the railway company to minimise the impact of construction and with the contractor to identify possible savings
Dan James, operation director for the Snowdonia Society, which is administering the appeal, said: "This opportunity should not be missed and we urge everyone who supports our campaign to contribute.
"It is essential that the present dilapidated building should be replaced with an unobtrusive, yet high quality Snowdon visitor centre which people of all ages and abilities will be able to use and enjoy."