For two months, a financial services firm in New Zealand cut its workweek to four eight-hour days but paid for five days—and invited university researchers to study the impact on performance. Very quickly, the results became clear: workers showed up on time and creativity burgeoned. Productivity rose 20 percent. The policy became permanent. The idea of a shorter workweek is even trickling over to America. Interestingly, the sports world is providing some of the best evidence that these types of changes may help.