As mmc stated, bns prefer to come out at night - as they are nocturnal, though not strictly so. If they're used to your presence, they'll come out even when you're around.
My bns started out very shy as well, scooting away when they saw a giant looming head drift towards them, but I fed them everyday and just watched them (and the tank) for minutes at a time, especially when I feed them, watching for a while after I drop something in. Also, when they ARE out, I tend to try and sneak up to them, so that I don't surprise them. I remember just lightly banging my fist against the table a few times and see all six of my bns going from swimming around casually to disappearing completely, within seconds. But yeah... then again, my tank is in my room, right on my work table, so it is possible that seeing me there a lot of the time, that got them used to me as well... not sure which of the above factors really coaxed them to become less shy, but I reckon it's a combination of trying to sneak up to them and not disturb them as much as possible, along with watching them... a bit. Makes them feel less insecure when you're around.