To set a reminder for an appointment, first double-click the appointment in Calendar to open its Appointment window.
To change the lead time for the reminder, click the down-arrow button to the right of the Reminder field and select the desired lead time from the list that appears.
Click the Save and Close button.
To help keep you on track, Outlook reminds you 15 minutes before any scheduled events. You can change the lead time for a reminder. For example, suppose you have an appointment that is 30 minutes away; in that case, you might prefer a 30 or even 45 minute advance reminder.
If you don't want Outlook to display a reminder before an appointment, uncheck the Reminder check box in the Appointment window.