This setting is available in your Settings --> Surfaces. If turned on, it will default the start time of the event to the sunset time for that day (rounded to the nearest 15 minutes, always rounded up).
It will also put an icon in the leads page when building a quote for the admin to hover over to see the sunset. This toggle determines if the delivery type specified will set the event start time to be at sunset, This is generally used for outdoor surface types for portable movie screen industries, but can be used for more than that.
