Before HighLevel, we were using a software called Motion to create and send calendar links. One nice feature within Motion was the ability to let the customer choose the duration of the meeting. For example, you could give 15/30/60 minute options and when they're booking the slot, it would allow them to choose the length of the meeting that they need.

Right now, there is a workaround where you could create a Group of those 3 different options, but it becomes clunky with creating multiple automation flows for each calendar, having to maintain and update 3x the number of calendars.

I could see this being an issue with showing available slots, but I think a simple solution would be on each time card to show the slots available (for example, if you had something at 10am and there is a 9:30 slot, it would show that 15 and 30 minute bookings are available at 9:30 and so on).