Are Roman Slave Work Hours Really Reduced?

My friend told me that Roman slaves only work 12 hours a week. Do you know if this is really true? I think I'd like to be a Roman slave in that case. Or maybe not. Is it possible that there were calls to reduce the work hours of slaves due to the fact that Romans were sometimes unable to find work because so much of the labor market was dominated by slaves? That doesn't sound right to me at all. However, I'm hesitant to say that it never happened.