Open the app and activate the menu in the upper right corner.
Scroll down to the top item "Ad Hoc Booking". Please activate the feature. (NOTE: It only works if you have choosen one calendar or disable the Calendar-Chooser.)

After you have activated the "Ad Hoc Booking" feature you can now complete the following properties:

"Allow Ad Hoc Bookings" - on/off
"Direct Booking" - Turn in 'on' if you have configured the room calendar directly, or off, if you have subscribed the room calendar
"Email for Invitation" - For a subscribed room calendar, you need the email address of the room which should be invited
"Ad Hoc Event Title" - Your Title which shows up in the calendar
"Header Label" - your creative text
"Background Color" - your decision
"Text Color" - your decision
"Button Text Color" - your decision
"Button Background Color" - your decision

Up to 3 Ad Hoc Event Times can be defined (Label / Time)
Left Button Label
Middle Button Label
Right Button Label

Left Button Time Period
Middle Button Time Period
Right Button Time Period

It is important to know, that only the buttons appear which are temporally also possible. A 15 minutes direct booking button does not appear if there are only 10 minutes left until the next appointment.

GOOD To Know: AdHoc Events can only be created and seen in the main calendar if your have write permissions to it