In Workfront, when inline adding a task, the default duration is 8 hrs
When you click the "New Task" or create a task via the API, the default duration is 0 hrs as the functionality requires you to set the planned hours.
The idea is that there would be a system setting that would allow each organization to set a default duration when tasks are created via the New Task button or the API, aligning the functionality with the current inline adding task functionality.