That is a good question Jeremy! I am happy to hear you are seeing progress with the plan and I think I can answer your question. The idea behind splitting the volume on the weekend into two pretty long run instead of one very long one is two fold. First, doing a single huge long run will take a more significant toll on you and requires more time to recover from. There comes a point where the volume hits diminishing returns for how much time you spend out there. Second, when doing two long runs there is an additional training stimulus that is introduced. The first of the two runs will deplete you metabolically and even with proper fueling and hydration you will start the second day in a fatigued and depleted state. This additional stress increases the benefit of the second run and magnifies the training stimulus. It is tricky to navigate how much is too much, and as you have seen the long efforts should be built up to and then spread out. I would highly recommend paying very close attention to post run fueling and hydration when you are doing the doubles. Also, don’t get pulled into the common trap in ultra running where people think that more is always better. Hopefully this helps!