I've used my debit card (as credit) within Japan and I can say they took that money out usually immediately. I did find a few places that were delayed at most 24 hours, but usually everything hit within that 24 hours.

So that makes me curious -- is it the bank just doesn't want to process the card transactions until they are finished, or is it a merchant problem?

But everyone's experiences are different, I'll be watching this and will update during my next trip to Japan in Jan.