It won't be 20 minutes.
It takes 20 minutes to do the charge. BUt there will be a queue of people. Normal throughput in a petrol station is what, maybe 5 minutes per car with 6-10 pumps? So for the same throughput you'd need 30-40 charging stations at each location.
Your applying petrol logic to an EV problem. Your forgetting that most people will not charge at public starters the vast majority of the time, especially rapid ones.
You can’t fill your petrol car at home/work/when parked but you can an EV.
Yes the number of charging points need to increase but only a fraction of cars are EV right now.
Just look at Norway as an example of a country that is years ahead of this issue. There are rapid charging hubs everywhere and they stretch all the way and well into the artic circle which is vastly more remote than north Wales. There are also slow AC chargers/3pin plugs everywhere and they are becoming ubiquitous.