Prior to the Great Recession temporary workers worked, on average, fewer hours per week than regular employees.
But as the chart below (from a NY Times Economix blog post) shows, this shifted in 2009 and temps now work, on average, 30 minutes more per week than regular employees.
I think this shift is an example of broader changes taking place in the economy as more firms increase their use of temporary and contingent workers.
BTW, another interesting tidbit from this chart is according to the U.S. Bureau of Labor Statistics, you need to work 35 hours or more to be considered full time.
This means on average the U.S. workforce is part time.