Open Outlook and go to the Calendar view
Select the date and time you want to block
Click New Appointment or New Event
Enter a title for the blocked time
Set the start and end time
Change the Show As status to Busy or Out of Office
Save and close the appointment
For a recurring block, choose Recurrence and set the pattern
To block a full day, create an all-day event
To block time on Outlook on the web, open Calendar, select a time slot, and create an event with Busy status
To block time on mobile, open Calendar, tap the plus button, and create an event with Busy status