Here's an update:
Every bit of exercise counts in reducing risk of early death: Study | CBC News

"Every bit of exercise counts in reducing risk of early death"

"The findings are good news for most Americans, who are becoming more sedentary and could break that up with short bouts of physical activity, he said.
"Take the stairs when there's the opportunity. Walk to the coffee shop instead of taking the drive-thru. Because that will all help you prevent bad health outcomes," he said. "Everything counts so take every opportunity."

The study also found that participants who got less than 20 minutes of MVPA each day had the highest risk of death, while those who did 60 minutes a day cut their risk of death by more than half. Those who did at least 100 minutes a day cut their risk of mortality by 76 per cent, according to the study."