Hey @lauramillerpics - It looks like the Seller whose link you provided is using our Online Store feature. They set up the photoshoot as an item and they used Modifiers to set up the time slots. My guess is that they set up each time slot to only have a quantity of 1 so that when someone checks out with that time slot, the system then marks it as sold out. This can all be done through your Square Dashboard.

Keep in mind that this Seller isn't using Square Appointments to do this so once someone purchases a time slot, it will not show up in your Appointments calendar. If you'd like to use Appointments to book one day, this workaround may be a possible solution for you.

Hope that helps clarify things for you!