Improvement needed to verify form submission when adding repeated slots and setting time range from and to is less than the "default slot duration" setting of the activity.

Suggestions for form validation and stop submission when the time range from and to is less than the default slot duration.

Replication:

1. Create a course.
2. Enrol two students.
3. Turn editing on.
4. Add a scheduler activity. Note that the default slot duration is set to 15 (minutes).
5. Visit the scheduler activity and click "Add slots", then "Add repeated slots".
6. While in the "Add repeated slots" page, tick "Enable" the setting Repeat time slots until, and set the date in the future (say one day or two days from today)
7. In the time range setting, set From: 00:00 and To: 00:10 (note it is just 10 minutes, compare it to the default slot duration of 15 minutes).
8. Click "Save changes" button.

RESULT: The page will refresh and the My appointments Slots page is displayed with the following message:
0 slots have been added.