Calendar allows you to add appointments that occur the entire day. All day appointments can occur for multiple days as well. For example, an appointment can occur for 3 full days. All day events appear at the top of the calendar in day view and occur from 12am to 12pm for the given day so there will not be any time displayed for the appointment.
An “all day” appointment that occurs for 3 days, no start and end times are displayed because the appointment lasts all day