FreeBusy offers you three default Appointment Types into Booking Page that can help you to quickly get started. Here is how you can update the duration in a Booking Page:

Step 1: Click on the "Edit Appointment Types" on a Booking Page.

Step 2: Click on "Edit Appointment Type" on an Appointment Type

Step 3: Scroll to section 2 "How long meeting should last?"

You can select multiple duration to offer as well. You could select let’s say select 30 minutes, 45 minutes and 90 minutes as possible meeting durations. This way your guest will be able to pick the meeting durtion as per their requirement.

Step 4: Click ‘Save Appointment Type’ to save your preferred choices.

Step 5: Click on Back button to go back to list of Appointment types.