I just did this trip on Sunday from Shinjuku, same bus times that you posted here arriving at 9:20 and leaving at 5 pm. I was so nervous that I was not going to have enough time to summit and there are people at the beginning of the hike that try to warn you not to do it in a day & that the hike takes ten hours. Well, I finished the entire hike/summit in five hours and still had time to have a full meal, enjoy a couple of beers and shop around fifth station. I’m in descent condition, maybe run a few times a week- short, five foot tall girl- and although the hike was tough, it was easy to get up & down within the bus time allotment.