With Redtail's Calendar, you have the option to set your default Start and End Times, so that you do not display times outside of when you schedule activities.
To set these, click on the Manage Your Account menu and select Change Site Preferences:
The second section you'll see on the Change Site Preferences page is Activity Management:
Click on the menu box to the right of Default Calendar Start Time or End Time to select from your available options:
After selecting your desired Start and End Times, click Save in the upper right hand corner of the Activity Management section and you will have successfully changed your Default Calendar timeframe.