I know that man-hours are used as a unit to measure time in things like modelling and other work actually done by people, but I also hear man-hours used to refer to graphics rendering time. How is that measured? If a video takes 200 man-hours to render, for example, what is that measured against? Obviously a person could not be expected to perform the mathematics necessary for rendering an image, but all definitions of 'man-hours' that I've been able to find refer to expected output of a human worker in an hour. How is that measured for things like video rendering which simply can't be done by a human?
I've never heard that term used for rendering before, but it is most likely referring to the number of hours of computation needed for a single CPU or GPU to process it. In most video and 3d applications, it is possible to parallelize the rendering of the video itself (though not necessarily the encoding.
Thus, a job that would take 200 "man hours" (more often called CPU hours when I've heard it used) would only take 20 hours if you had 10 CPUs working on it.