It depends how clean/shiny you want the razor to be. I have a few resto's that took 14hrs sanding on 180. Once you finish with 180 it goes a bit faster. Sometimes I leave a little discoloration, but that's coz I'm not too fussy, and it leaves a little character on the blade.

Yours looks like it could easily have another few hours at 180. It can be quite slow and arduous, but in the end, its worth it.

Good luck, look forward to seeing the razor once finished.