when a BTA moves behind a rock when you first introduce it, then, yes, leave it alone. however, BTAs can be quite stupid creatures and sometimes they WON'T move, even when they need to. so I usually like to give them about 3 days, and if they're still hiding, then I will take them out and move them out to the open.
you should definitely start moving that guy out and feed him, otherwise, he will just shrink and start deteriorating away.