I’d expect large plantations to have records of how many slaves they own and production numbers. Perhaps one could extrapolate from that an estimate of labor hours per slave, but individual slaves’ productivity and hours worked, I’d be surprised if this was possible. Smaller scale slave owners might not have been so meticulous about record keeping and much documentation may be lost to time. It is regarded as a shameful institution today, discouraging holding on to such things.

I’m interested in what you find!