Do you want most of your new appointments to use Free (or Tentative or Out of Office) as the default for the "Show as time" instead of Busy?
Outlook doesn't have an option to set the "Show time as" default but you can create a custom appointment form with "Show time as" set to Free, Tentative, or Out of Office, then publish it and set it as the default appointment form.
How to create and publish a "Free Time" custom form
First, go to File, Options, Customize Ribbon and add a check to Developer ribbon on the right.
Step 1: Go to the Calendar folder
Open the calendar folder you want to publish the form in. This makes it easier to publish the form because it gets published to the folder you are "working" in.
Step 2: Create custom appointment form
Open a new appointment form and change Show as time as desired.
Step 3: Publish the form
Step 4: Set the new form as default for new appointments
Now when you create a new appointment, the Free/Busy time will default to your desired setting, Free in this example.
Multiple Calendar folders
The form is published to a Calendar folder and the default applies only to that Calendar. If you use multiple calendars you need to set the form as default for each calendar.