David M., 44, in a hurry to send a payment that was not in any particular hurry, selected the fastest available fee on Thursday, paying roughly $40 to shave an estimated six minutes off the wait.

He then spent those six minutes, and a further forty, refreshing the transaction and refreshing his balance, in the manner of a man guarding a kettle.

"I didn't want to risk it," David explained, of a transaction at no risk. He had been offered a quarter-dollar fee and a one-hour wait. He chose otherwise, decisively, the way one books a fire engine to cross the street.

The six minutes were saved. They were also, immediately and with interest, spent.