We've made some changes to how we handle the times on the appointment form.
Previously, when making a new unavailable block the default duration was the duration of the practitioner's default appointment type. The default duration of a new available block was 1 hour. However, when you changed the start time, the end time would be changed to 30 minutes later.
We have now made 30 minutes the default duration for unavailable and availability blocks. This default is applied when opening a new block and when the start time is changed.