The unpredictable hours working as a research scientist put pressure on other parts of her life.

''It means it's quite hard to meet up with people for dinner, it makes it quite stressful to finish in time for dinner,'' she said. ''The main thing is just the exhaustion and that so much of your life is taken up by work that you don't have the mental space for other things.''

A report to be released on Wednesday by the Australia Institute points to some of these pressures on workers. About a fifth of the 1495 people surveyed said they had little idea when they would finish work each day. If that was carried across the entire workforce it would be more than 2 million people.

Those who worked ''unpredictable hours'' were at least twice as likely to say their work had an effect on their health, mental wellbeing or relationships with friends and partners. There was also much higher reported levels of anxiety.

For Dr Smith, a typical working day begins at 7am and most days run for 12 hours. Sometimes she is still at work at the Victor Chang Cardiac Research Institute in Darlinghurst doing experiments well after dark.

Her work - looking at new genes that could be used to treat high blood pressure - is something she loves. It has taken her from Melbourne, where she grew up, to working overseas and now to Sydney. But if a 12-hour experiment is under way, you can't just knock off at 5pm.

The Australia Institute executive director, Richard Denniss, said this was the fourth time the institute had looked at issues around working hours as part of its Go Home On Time Day, which falls on November 21. He said the issue of unpaid overtime and long hours were persistent.