Classic Outlook
Select File > Options > Calendar > Calendar options
Check the Shorten appointments and meetings checkbox and select End early or Start late, depending on what you want.
Use the drop-down to select the number of minutes for meetings less than one hour and one hour or longer, then click OK.
New Outlook
You can set events to end early or start late by using the following instructions.
Select Settings
> Calendar > Events and invitations.Select the Shorten duration for all events checkbox.
Use the dropdowns to select the number of minutes for events less than one hour and one hour or longer, then select Save.