The Multiple time period field is only used in the form builder for related entities, not for event, profile or database forms. This field allows you to enter start and end times for days of the week and is used to determined availability of a related entity for the scheduling and appointment tools.
The example above shows a related entity for a physiotherapist. The related entity is used in an appointment form for physiotherapy bookings. The related entity uses a Multiple time period field named Availability to indicate the hours that Jessica Ritz is available for appointments. For example, she has indicated that she is available on Thursdays from 3-6pm.
When someone wants to book an appointment with Jessica, her available times will be shown on the Enter appointments tool, with all other times greyed out. The example above shows Jessica's availability on a Thursday, where she is available between 3 and 5:30pm. Note that the 5:45pm slot is not available because the appointment form is set up (in the advanced properties) with a minimum duration of 30 minutes, so 5:30pm is the latest appointment that accommodates this.
Since related entities can only be updated in the builder interface, weekly availabilities recorded with a Multiple time period field can only be updated by your Smartabase builder. If a related entity's availability changes each week, the builder will need to update it accordingly.
If you create a related entity and do not fill out the Multiple time period field, the entity will always be shown as unavailable in the planning tools.