Academic Settings / Marking Settings / General Settings / Assessments & Assignments / New Assessment Configuration / Use timetable periods when you schedule an Assessment/Assignment
If this setting is enabled, then the end user has to select a timetable period when he/she schedules a new assessment or exam.
If disabled, then the user can select start and end time freely.
Setting -> Active
When scheduling a new Assessment or Examination, the choice of time is based on the timetable 
Setting -> Inactive
The choice of time is free 
