Duration (project management)

Duration of a project's terminal element is the number of calendar periods it takes from the time the execution of element starts to the moment it is completed. 
Duration should not be confused with work. E.g. it takes three days for a snail-mail letter to arrive at point B from point A, whereas the work put into mailing it may be 0.5 hours. 
Strictly speaking, the phrase "Duration of terminal element X is 5 days" is incomplete. It fails to specify the following:
So the improved statement could read:
It may seem unwieldy to use such complicated statements, but lack of detail often leads to misunderstanding. 