That’s considerably slower than the most common response time of two hours, with the fastest councils aiming to act within minutes.
Hitting a pothole, or even swerving to avoid one, can ruin a car’s suspension, steering or tyres, according to the AA.
In extreme cases they can cause serious accidents.
In 2018, the AA estimated potholes cost drivers and insurance companies an eye-watering £12 million.
It said: “The pothole epidemic has become nothing short of a national disgrace.”
A Freedom of Information request by the RAC found that Leeds City Council determines how dangerous a pothole is by measuring its size and depth.
The local authority will only investigate potholes that are at least 4cm deep.
That applies regardless of whether the pothole is on a quiet lane or a major route.
The RAC Foundation recommends a different approach, assessing the impact of a pothole on road users over size.
Director Steve Gooding said: “The total number of potholes being filled in might still be limited by a shortage of funding, but this approach at least means those that are most dangerous are fixed first.
“Those particularly vulnerable to potholes – cyclists and motorcyclists – might ask whether the speed of pothole investigation should be based solely on the risk to users.”
The Local Government Association called for more funding for council-controlled local roads.
Transport spokesman Councillor Martin Tett said: “Keeping roads safe for all users is one of the most important jobs councils do.
“That’s reflected in the fact that local authorities are fixing a pothole every 21 seconds.”
He added that councils need “consistent and fairer government investment in local road maintenance”.