The duration of an activity or task is how long it will take. There are two ways to measure this. The first is how long the task takes to perform, usually in terms of "staff time" or "effort". The other way to measure the duration, and that is "elapsed time".
So for instance it make take 15 hours from staff with the expertise level assigned to the project. This could be allocated multiple ways: three people working simultaneously for 5 hours each, one person working two hours per day over eight work days, or 15 people each putting in one hour sometime during a week.
|Who and When||Staff Time||Elapsed Time|
|three people working simultaneously for 5 hours each||15 hours||5 hours|
|one person working two hours per day over eight work days||15 hours||8 work days|
|15 people each putting in one hour sometime during a week||15 hours||1 week|
Related: estimate activity durations