Perform the following steps:
Choose File -> New -> All Day Appointment. An Appointment window is displayed, with the All day event option selected. The Appointment window is similar to that displayed when you choose File -> New -> Appointment, except that the start time and end time are not displayed.
Enter the appropriate details in the Appointment window, as described in To Create a Standalone Appointment.
Choose File -> Save and Close.
Email and Calendar saves the all-day appointment and then closes the Appointment window.