A Third of Millennials Don't Last 90 Days in a New Job According to human resources expert Greg Weiss, 1 in 3 millennials don't make it through their 90-day probation periods. Millennials are more likely to under-perform, be late or absent or switch jobs. Social media-induced envy appears to play a role in these patterns of behavior. Greg Weiss, via 'Daily Mail' Greg Weiss, via 'Daily Mail' Glassdoor reviews heighten scrutiny among prospective millennial job applicants. But Weiss says the stereotype of millennials being lazy is just a misconception. High turnover can also be blamed on lack of job training and on-boarding resources.