Jack Dorsey puts in a standard eight-hour workday -- at each of his two jobs. He starts the day at Twitter, where he's the chairman, then heads over to Square, where he's the CEO. The offices are two blocks apart in San Francisco. "The only way to do this is to be very disciplined. I theme my days ... There's interruptions all the time, but I can quickly deal with an interruption and know 'it's Tuesday, I have product meetings, I have to focus on product stuff.'" After a week of 16-hour days, Dorsey does relax on weekends, dedicating Saturday to hiking and Sunday to "reflection, feedback and strategy" (sounds like work to us).