How long is the OP going to stay in Japan?

I find that if you are only staying for a week, it really doesn't matter. You will have jet lag but the excitement of seeing new things will keep you running.

We do the YVR - KIX / WNZ route regularly. We arrive late afternoonish and we struggle to stay awake until about 9 pm when we crash. We find that keeping hydrated really helps and on the plane we refrain from any form of caffine. If we fall asleep on the plane, we are great but if we don't we don't fret about it.

Just have a good time - keep active during the day and you will be fine.