Councillors granted Ecco Wash Limited planning permission to operate in part of the car park at Antelope Park in Thornhill in April last year.
This approval included a condition limiting the operation to 8am to 6pm, which was stricter than the 7am to 7pm suggested by officers.
Members of the planning and rights of way panel decided to impose the shorter hours to protect the living conditions of residents in nearby Linacre Road, who had raised concerns about noise disturbance.
The business launched an appeal to the Planning Inspectorate.
A government-appointed planning inspector considered the case and decided to allow the appeal.
The decision notice published this month said the impact of the car wash needed to be assessed within the context of the site, which is a busy car park on a retail park.
The inspector said a noise assessment report submitted with the application indicated the impact would be “low” and “less than adverse”.
Southampton City Council had not disputed the methodology used and results of the assessment report, and it had not provided any substantive alternative survey evidence, the inspector said.
The decision notice said: “I therefore conclude that there is no cogent evidence before me that the proposed increased operating times of between 7am and 7pm Monday to Sunday would materially harm the living conditions of neighbouring residents in Linacre Road, having particularly regard to noise disturbance.”
Reacting to the successful appeal, an Ecco Wash spokesman told the Local Democracy Reporting Service: “This is a win for common sense and for our customers.
“Extending our daily hours to 7am to 7pm finally provides the improved flexibility that Southampton’s commuters and Antelope Park’s customers demand.
“The ruling restores the operating hours originally supported by the technical evidence and the council’s own planning department.
“It confirms that our facility, which features enclosed bays and a three-metre high acoustic barrier, is a low-impact use perfectly suited for a busy commercial hub like Antelope Park.
“We are pleased to see the evidence-based approach upheld, allowing Ecco Wash to better service its customers while remaining a responsible member of the local community.”