I did it a long time ago when I was a lot younger. We started from Yoshida-guchi on a Sunday morning in early October. Got to the 5th station around 5pm. Then started to the top around 4am Monday morning. Didn't see anyone on the mountain either day except a few at 5th station coming down from a Sunday climb and then two people at the top who had over-nighted at the summit. There was about 5 or 6 inches of snow above the fifth station so on our descent, we ran down from the summit to the 5th station in about 20 minutes. Think running down a sand dune. It was pretty fantastic.

Hiking from the bottom is definitely worth it if you have time and stamina although it's tree covered so there's not much of a view.

I would totally avoid July or August. The crowds are horrific. Weekday in mid-September is best. If you don't have any choice on dates, I'd choose another mountain.