The quote goes back to James Whistler when he was being cross-examined at a trial. He sued a journalist for libel who had written that he "never expected to hear a coxcomb ask two hundred guineas for flinging a pot of paint in the public’s face"—a pretty good line in its own right, but unfortunately for the journalist, he was up against a wit with superpowers. The exchange at trial:
Lawyer: Oh, two days! The labour of two days, then, is that for which you ask two hundred guineas!”
Whistler No;—I ask it for the knowledge of a lifetime.
Whistler won the trial, was awarded a farthing, and had to pay his own legal fees.
https://quoteinvestigator.com/2018/01/14/time-art/
https://quoteinvestigator.com/2018/01/12/lifetime/