Appointments+ problem with minimum time increment

Under Settings--->General I've set a time base of 5 minutes (my client has a minimum session of 5 minutes). However, when I save the settings there is a pink message at the top:

"One of your services has a duration smaller than time base. Please visit Services tab and after making your corrections save new settings."

But when I to the the Settings tab, I am only able to set 30 minute increments for a service - not the 5 minute increments my client needs.

Are my settings wrong or could this be a bug?

Thanks for your help!