Do you mean man-hours/unit, or man-hours per unit?
As you suspect this is the expected "normal" time to do something to one unit. For example, an installation manual might state:
"Installation will take 4 man-hours/unit."
This means that an experienced technician would be expected to take four hours to complete the installation. Or two technicians would be expected to do the job in 2 hours.
Of course 9 men and 1 women can't make a baby in 1 month.