1. Select the Calendar icon at the top of the compose window.

2. You can choose to view your calendar that day, over the course of 7 days, or you can set a custom date range. 

3. A pop-up will appear with your availability, select the appropriate dates and times here.

4. Once you have completed this step, select Done. Your availability will show in the message body.

5. To change your time availability, go to Calendar Preferences.