Yes, you do. You can contact them on twitter to visit. They post their schedule for the year late at the end of the previous year I think. So you can see what days WILL be open, and which will be open with appointment.

Other than that, be prepared to plan out your train route ahead of time. If you are coming from Tokyo(which I think most foreigners will) it's a non-insignificant ride there. Determine how much time you'll need to get there, and plan according to their hours.