Hello,Is there a possibility of open ended appointments?

Hello,Is there a possibility of open ended appointments, where the person booking selects a start time and a duration?

At the moment, there is no option for the person filling the form to select the duration. The duration and time are set from within the field's properties and by the form owner:

If you want the person who is filling the form to set the time and duration, then you can use a basic time form field and a Date Picker field on the form:

Would this help out?