Modify your Event’s Start and End Dates and Times:
You can easily schedule an all day event by placing a check in the All-day Event checkbox. When All-day event is selected the event start and end time fields will be removed from the New Event window and the date of the All-day Event will be shaded on your calendar, thus indicting that you are busy for the entire day. All-day events can be used to indicate to others that you are unable to accept any events for the day, or that you are attending an event that will last the entire day.