I would like my Outlook calendar to always show myself as busy for the next 24 hours. The goal is to prevent people from scheduling a meeting for the same day. Is this possible?
Create an event/appointment in Outlook, but not as you'd expect to.
If you set it as an All Day Event then it goes to the top of the calendar, and annoyingly people will probably not notice it and thus book appointments for you.
So what I suggest you do is make an appointment from 00:00 to 23:59 then you won't have to update it every half an hour, or I have I got the wrong end of the stick?
Once you have done this you can copy by holding Ctrl and pressing C, click on the next day and paste holding Ctrl and V