In New Zealand, insurance company Perpetual Guardian reported a fall in stress and a jump in staff engagement after it tested a 32-hour week earlier this year.
Even in Japan, the government is encouraging companies to allow Monday mornings off, although other schemes in the workaholic country to persuade employees to take it easy have had little effect.
Britain's Trades Union Congress (TUC) is pushing for the whole country to move to a four-day week by the end of the century, a drive supported by the opposition Labour party.
The TUC argues that a shorter week is a way for workers to share in the wealth generated by new technologies like machine learning and robotics, just as they won the right to the weekend off during the industrial revolution.
"It would reduce the stress of juggling working and family life and could improve gender equality. Companies that have already tried it say it's better for productivity and staff wellbeing," said TUC economic head Kate Bell.
A recent survey of 3000 employees in eight countries including the US, Britain and Germany found that nearly half thought they could easily finish their tasks in five hours a day if they did not have interruptions.
Schulz-Hofen, a 36-year-old software engineer, tested the four-day week on himself after realising he needed to slow down following a decade of intense work launching Planio, whose tools allowed him to track his time in detail.
"I didn't get less work done in four days than in five because in five days, you think you have more time, you take longer, you allow yourself to have more interruptions, you have your coffee a bit longer or chat with colleagues," Schulz-Hofen said.
"I realised with four days, I have to be quick, I have to be focused if I want to have my free Friday."
Schulz-Hofen and his team discussed various options before settling on everybody working Monday to Thursday.
Clients who call on a Friday hear a recorded message explaining why nobody is at the office.
"We got an unexpected reaction from customers. Most of our clients did not complain. They were just jealous," Schulz-Hofen said.