How long in fridge for sushi steaks?
I have always made sure that I only defrost enough to meet the needs of the moment for sushi.  If you cut the blocks into 4 to 8 rolls worth, they should defrost under running water in just fifteen to twenty minutes, just about the time it takes me to do a batch of sushi rice.  That said, fish once defrosted will start to lose flavor immediately but will remain edible for 2 days.  Once it starts to smell, get rid of it immediately, and I would play it very safe on that "starts to smell" the faintest whiff should be enough to send it to the bin.