With Redtail's Calendar, you have the option to set your viewable time increments in 15 minute, 30 minute or 60 minute slots.
To set these, go to your Preferences:
The third section you'll see on the Preferences page is Calendar Management:
Click inside the Default Calendar Time Slots box to select from your available options of 15, 30, or 60 minute slots.
After selecting your desired Calendar Time Slots, click Save Preferences in the upper right hand corner of the Activity Management section and you will have successfully changed these.