In Calendar 365 the default time slot for any activity is 30 Minutes. To change the default slot and create different time slots for activities, navigate to Configuration → Views → Slot Duration. In the Slot Duration, you can select different time slots from 15, 30, 45, 60, and 90 Minutes. Select any time slot and click on Save to save the changes. Now if you create an activity it will have your selected time slot.