So you mean, if I sell my town (assuming there is no 'saving, do not turn off the power or reset') screen, I have four minutes to shut the system down and my old town will be intact?
It takes four minutes to get through Nook's spiel and then through Rover to pick a map if you're map resetting. You can back out of the sale of your town at any point as long as you don't go into a new map and plant the town tree. So, four minutes was referring to the amount of time it takes each time if you are looking for a good map after talking to Nook about selling your town, and not that you have a deadline of four minutes in order to preserve your original town.