At what point during the development of your dissertation did you begin to struggle with statistics? In my view, statistical considerations come into play almost as soon as you have developed a topic. For all practical purposes, a statistical consultant is probably not necessary until you have spent time developing the topic and doing some literature review.
But the point I am making is, as soon as you start focusing your topic through the development of research questions, that can be a crucial turning point in terms of the complexity of your study. Many of my clients came to me only after they had developed rather convoluted research questions and developed their literature review accordingly. When I advised them of ways to simplify their research questions, they realized they had unnecessarily complicated their study. Of course they were open to simplifying their research questions and methodology, but they could have saved themselves significant effort had they contacted a statistician sooner.