You can set a default appointment time in your account so that appointments will book for the time you set. You can always change individual appointment times or set appointment times with appointment profiles.
To set a default appointment time:
1. Go to Account > Settings and click on the General tab. 
2. Select number of minutes with the (
) arrows. 
3. Scroll down and select 
to save your changes.
With this set, all new appointments created will automatically be set to the time that you entered.