You can space your availability 15-minutes between each hour. For example, available from 9 - 9:45, unavailable from 9:45 - 10:00. repeat this schedule for each hour and day. You can set your schedule to repeat and you will not have to set it again.
You can also advertise a 45-minute session, but set the session for 60 minutes.
You will also want to sync your Yondo calendar with your Google calendar, when you book a time on your Google calendar it shows you as unavailable on your online Yondo calendar. Here is an article on how to sync your Google Calendar.