There are some of the study programs within ADF that do require the observation of the High Days, and even that doesn't require ALL of the High Days be ADF ritual (Dedicates Program). But outside of study programs there are not many requirements placed on private practice. So if you are an ADF Druid that works as a solitary and you are say of a Hellenic hearth culture, there is no reason what so ever that you MUST following 8 High Day rituals. Matter of fact if you are a solitary participation there is no reason you have to stick with the Grove mandate of Indo-European cultural deities either. ADF is not in the business of controlling what people do in their private practice, even in Public practice there are only loosely controlled guidelines.
Thomas, Kirk. Kirk-Fire.jpg.The Druid's Progress. Google Image Search. 1/17/2013. http://www.druidkirk.org/photos/Kirk-fire.jpg