Not a new owner, he opened it 12 years ago.
Based on my experience, there is zero difference in the time to process a cash or charge purchase. With the charge you have to wait for the customer signature copy to print, the store copy to print, the customer to sign the slip. That takes AT LEAST as much time as making change. However, I generally phone in my order and they give you the total then, and I have exact change available, so my cash sale is probably quicker.
But what do I know, all I know is the merchants that take both cash and charge say they make more on a cash sale and I think they would know.