The admin calendar has the ability to be zoomed in and out to adjust the duration of the time intervals. This allows you to compress or expand the length of appointments and view the calendar times as blocks of 5, 10, 15, 30, 45, 60 or 90 minutes. 

This is useful if your appointment durations are short, for example 10 minutes, since you can then see and select times on shorter intervals. The calendar default zoom is 15 minutes.

The zoom controls are located on the top right corner of your admin calendar, the +/- icon.