How much time does resting using one of those things pass? Does it even pass time? After killing something (that's not a carrion eater), how many times do you have to rest at a bench to have it reliably respawn?
I don't really know myself, but apparently it only counts as half a day with resting benches. That's just something I read somewhere. Just leave BBI and rest somewhere in Gransys to respawn the enemies, then ferrystone back to BBI.
I don't think there is a day/night cycle and I'm not sure how the time pass thing works. Time does gradually pass, I've noticed chests respawning while on daimon runs but in order to be sure of respawning the dark bishop for instance I always go back to casardis and rest.