Freedom of information requests provided by NHS Lothian last week said one patient had waited six hours and 20 minutes to be seen between February and March this year, at the Wester Hailes Healthy Living Centre.
The service opened in February and was the first of around 30 clinics pledged by the SNP in an attempt to end the “8am rush”.
But NHS Lothian said an error occurred in its admin entry that was not signed off until the end of a shift, resulting in the “appearance” of a six hour wait.
The health board said the longest wait was actually two hours and 48 minutes, while the average was 38 minutes.
The SNP has said the new figures are a sign of “success”.
Tracey McKigen, director of primary care services, NHS Lothian, said: “A recent freedom of information response issued by NHS Lothian suggested the longest wait time at our GP walk-in clinic at Wester Hailes was six hours and 20 minutes. This was incorrect.
“The mistake was due to an administrative recording process which resulted in the appearance of a wait of over six hours.
“In fact, the individual concerned was seen within the hour. The average wait time at the clinic is 38 minutes and the longest wait was two hours and 48 minutes. We would like to apologise for the confusion that has arisen as a result.”
Dr Sandesh Gulhane, the Scottish Conservative health spokesman, said: “If this was a genuine mistake, it is further proof that Scotland’s NHS is still living in an analogue age because SNP ministers have refused to move with the times.
“Frontline medics have been clear that John Swinney’s GP walk-in centre gimmick is simply not working in reality. Patients are experiencing unacceptable long waits for treatment because there aren’t enough GPs to staff them.
“If the nationalists win the election, our health service will continue to fall into disrepair. That’s why you need to vote Scottish Conservative on your peach ballot to stop an SNP majority.”
Simita Kumar, SNP candidate for Edinburgh South Western, who has also worked in Scotland’s NHS, said: “It’s hugely welcome to see these updated figures which show what a success the first GP walk-in centre has been already – with close to a thousand patients treated in the first month.
“I trust that the opposition parties who were desperate to knock GP walk-in clinics last week will now be just as quick to recognise the success it has been and support the rollout of the clinics across the country.
“The SNP’s plan for the NHS is working – waiting times are down for ten months in a row, operation numbers are up and we are now opening GP clinics all over Scotland. A re-elected SNP government, under John Swinney’s reliable leadership, will work tirelessly to carry on improving Scotland’s NHS.”
The BMA has said the services offer a fraction of a standard GP surgery but at a significantly greater cost.
Dr Al Miles, deputy chair of the BMA Scottish GP committee, said: “BMA Scotland has warned that from what we know from the experience of walk-in centres used elsewhere in the UK, there is no convincing evidence they reduce pressure on GP practices, out of hour services, or emergency departments.
“General practice in Scotland is hugely stretched and we recognise patients can currently face a struggle to access services in a timely way.
“However, as these figures suggest, it is highly doubtful the introduction of these walk-in centres will have a significant impact on improving access or ending the ‘8am rush’ for appointments.
“Walk-in centres offer a fraction of the services of a standard GP surgery, at a much greater financial cost. We cannot afford to be directing funds into projects which have already been unsuccessfully tried in England for over 15 years – this funding would be far better targeted at existing GP services, which we know will deliver the best care for patients.”