He's the chief executive of a billion-dollar start-up, but that doesn't mean he works past 5.30pm.

Stewart Butterfield's company Slack has the internal mantra of "work hard, go home."

Business Insider reported Butterfield told a press conference on Friday that people who work 8 hours are more focussed at work.

"The most productive employees from my experience are those who go home at 5:30pm, but are hyper-focused at work," Butterfield said. "People can only think really hard for 6 to 8 hours a day."


Butterfield's Silicon Valley start-up Slack has about 350 employees and is valued at US$2 billion after just over two years of operation. He sold his photo-sharing start-up Flickr to Yahoo in 2005 for US$20 million.

Butterfield said it wasn't easy to be productive at all times and Slack can make workers more productive than ever before.

A chat bot that removes the need to open up another app to see information could advance productivity, Butterfield said, according to Business Insider.

Butterfield told media he saw a future where Slack became smarter and more intelligent as it gathered data, eventually automating some of the most repetitive tasks, like finding who's leading what project.

"Having a bot allows you to immediately answer those questions," Butterfield said. "It's incredibly powerful."

"It's an opportunity for us, where Slack becomes the browser and the command line for the enterprise."

Slack recently surpassed 3 million daily active users, and most of its customers are small teams or businesses.