By default, the time increment for per-minute bookings is 15 minutes. That is, by creating a thirty-minute booking, the availability will still show as 8:00; 8:15; 8:30; 8:45; etc.
On the contrary, by enabling the option Time increment based on duration, the increment will be the same as the booking duration. Therefore, for a thirty-minute booking, the times shown will be 8:00; 8:30; 9:00; 9:30; etc.
Moreover, you can also enable the option Time increment including buffer that adds the buffer to the time increment based on duration.
We created a thirty-minute booking and set the Buffer to 15 minutes. We activated both options Time increment based on duration and Time increment including buffer.
The availability will consider both the booking duration (30 minutes) and the configured buffer time (15 minutes) and will show as below.