Marissa Mayer debunked this in 2013: http://www.businessinsider.com/mayer-google-20-time-does-not...

"It’s funny," she said. "People have been asking me since I got here, 'When is Yahoo going to have 20% time?'"? "I’ve got to tell you the dirty little secret of Google’s 20% time. It’s really 120% time."