...check the frame by frame sequence presented in the book (viewed from behind) as well as the other evidence he presents, you will get the best perspective on when Hogan performed the slide of the hips. What the author oint out (through the same line drawing you are using, only from behind) is how Hogan moved the center of gravity over the pivot point (later in the BS but still before the DS)before he made his downswing. This eliminated any slide during the actual DS and thus eliminated the timing it took to get in the proper impact position with a slide. This film frame sequenc is the only video I've seen that provides a clearer indication of what he was doing.
As on any forum there are differnces of opinion and each is left to conclude what he/she wants.
Bennet and Plummer teach getting in the same positon but with a tilt of the spine, which for some is difficult to perform if you have flexibility issues.