Voters turned out on Saturday after months of political haggling and violent protests for the poll - touted as the completion of the mineral-rich West African country's transition to democracy after a 2008 coup.
A spokesman for the national electoral commission (CENI) had originally suggested provisional results would be ready on Tuesday, 72 hours after the long-delayed legislative election.
However, CENI Vice President El Hadji Ibrahim Kalil Keita said on Tuesday the commission had until within 72 hours of the arrival of the last voting sheets from polling stations to announce a result. With sheets trickling in from some 12,000 sites across the country, that could take several days.
Sidya Toure, leader of the opposition UFR party, said that his supporters would wait for the results to be officially announced but they would not accept any attempt to tamper with them.
Guinean media have in recent days covered tallies of results posted on voting stations from across the country. The piecemeal figures suggested a strong showing by President Alpha Conde's RPG party, Toure's UFR and the opposition UFDG led by Cellou Dalein Diallo.
"We have all the results and the international observers have them too. We will not accept rigged results," Toure told Reuters. "If they do not reflect the will of the people, we will reject them."
No party is expected to win an outright majority in the 114-seat National Assembly and coalition-building is expected in the aftermath.
In a country where the president holds real power, the election is seen as a rehearsal for the 2015 presidential race when Conde's five-year term ends.
A European Union observers mission on Monday said CENI had failed to fully correct problems with the voters list and urged the commission to publish results on a bureau by bureau basis to make them as transparent as possible.
Moustapha Naite, spokesman for the ruling RPG party, said it had "cleaned up" at the election and the opposition was trying to twist the outcome.
Political analysts say any dispute over the election results could plunge Guinea - the world's largest bauxite exporter - back into the political violence which left some 50 people dead and deterred mining investment.
"The government must understand that it is in its interests to preserve the integrity of the electoral process to anchor democracy definitively in this country," said Alpha Amadou Bano Barry, a university professor.