I've had him for about a month. I had previously had a different dwarf puffer in the tank, but that one succumbed to internal parasites. There were a few pest snails, which had been the first one's primary food. I just deep cleaned the tank, so there aren't any left in it. Hopefully it will start to associate me with food.
I also changed my decorations and plants (all fake) around a little bit, so there are still hiding places, but there is more things to explore, so hopefully that will help too.