If you use the book’s pace of 4 MPH, which is actually what many people would consider a brisk walk, would take 75-100 hours, or around 3-4 days. That’s a long time to stay up without sleeping, let alone being physically active the entire time. I’d guess someone who is reasonably fit might be able to do half of that before collapsing. Perhaps someone who was using drugs or doping might be able to do it.