Yeah, I'm studying at least that much right now. I think that even if you don't end up doing anything new for the day, you should at least doing your review cards (if you're using SRS/flashcards, which you should be). That is what I do on Niko's suggestion and it keeps you from falling behind while doing something that it somewhat less intensive.

Have a good time in Japan! I had a great time when I was there a few months ago and I'm going to be going back again in the near future unless something changes to prevent it. Maybe I'll see ya there ;P