One of the most consistent findings in REST is how many really prolific and creative people do their most important work in about four focused hours a day. They’re not taught that this is a magic number; they often start their careers as workaholics; and some find this sweet spot when they’re younger, others when they’re in middle age of later.
Add Kurt Vonnegut to this list, as Literary Hub contributor Emily Temple notes in this piece on “Kurt Vonnegut’s Greatest Writing Advice:”
I get up at 7:30 and work four hours a day. Nine to twelve in the morning, five to six in the evening. Businessmen would achieve better results if they studied human metabolism. No one works well eight hours a day. No one ought to work more than four hours. (From an interview with Robert Taylor in Boston Globe Magazine, 1969)