How long a layover before British Airways/Qantas puts you up at a hotel?

I have an 8 1/2 hr layover at Narita airport. BA flight connecting to Qantas Business Class. My ex suggested i would be put up at a hotel because it's so long, but others have said it's unlikely. how would i find out? I know i'll have access to the Qantas Club lounges, but I'm considering venturing into Tokyo for a couple of hours because I've never been to Japan, but am somewhat concerned about getting lost, even with the Narita Express train.