Yes, when relating to a person-hour to work, it is a general concept that is supposed to be used within context. There is always the classic counter-example: Nine women cannot have a baby in a month. However, a large project with discrete components can often be sped up with more people. To a limit.
Of course, if you are rating life support in terms of person-hours, then such considerations fade away. Nine women really will use up nine person-hours of air in one hour. Or, if one of the women immediately kills the other eight, she would get all nine hours of the air.