I think the EdD is more often based round practical things, involving action research and classroom work, etc. and may have more taught areas, whereas a PhD in an area of education may be more theoretical and therefore more like any other PhD in the humanities. I don't think there would be much difference in the amount of time needed overall, but the pattern of the work may be different For example if the EdD involves work directly with children you may need more time actually in schools, so you could find your work dictated by school terms and this would in turn affect the rhythm of the workload to a greater extent than a PhD in another area with no such restrictions. My research is in education, but not directly linked to the pupils, so I have the opposite problem, I work harder on my subject during the holidays as during term time I have more things to do relating to my work in school. you may find it more useful to look at it from this angle as it may give you an idea which pattern will be best for you.