You can edit or delete a class timing set through the option Manage class timing sets. YOu need to clear all the dependencies beforehand.
Editing a class timing set - You can edit a class timing set at any time, however, only the existing class timing records can be edited. You cannot add new class timing records.
Deleting a class timing set - You can delete a class timing set only if it not used when creating a timetable for the batch.
At the top of your dashboard, click the module access icon > Academics > Timetable > Manage class timing set to open the Manage class timing set page.
To edit the name of a class timing set, click View class timings and then edit the name of the class timing set.
To edit or delete a class timing record, click View class timings and then edit or delete the name of the class timing record.
To delete a class timing set, click Delete.