I recently developed an issue with printing my boss' calendar (no problem printing any others).  When I print preview, the 30 minute minutes/appointments appear as 60 minutes however it is color highlighted on the left for the 30 minute period.  The same issue exists when I actually print the calendar.  When in regular view, it appears correct. I compared settings with my calendar and nothing appears any different.  We have installed the calendar print add-on but that doesn't seem to help.

We use Outlook Exchange.

Hi,

According to your post, I understand that the 30 minute meetings/appointments appear as 60 minutes and it is color highlighted on the left for the 30 minute period when print calendar.
If I misunderstand your concern, please do not hesitate to let me know.

Which Outlook version are you used? How about change another Outlook client for testing? Also try to update Outlook to latest version.
I find an similar thread about your question, please refer to: https://social.technet.microsoft.com/Forums/office/en-US/bff3012d-2c64-4add-a0e7-da754a3c16e9/outlook-2010-30-minute-calendar-appts-show-as-1-hour-appts-in-print-preview-and-when-printed?forum=outlook

If this issue only occur on Outlook client, I recommend contact Outlook IT Pro Team so that you can get more professional suggestion.
For your reference: https://social.technet.microsoft.com/Forums/en-US/home?forum=outlook&filter=alltypes&sort=lastpostdesc