Since the fish are still adjusting to the tank, I'd give it another week or so. I could go back and read your previous threads, but I am on dial up and that's WAY too time consuming. How did you cycle the tank before adding the labs? If the tank isn't cycled, Africans will hide. They are generally always out and in the open, so only a few situations come to mind as to why they hide.
1) Uncycled tank
2) High nitrates/Nitrites/Ammonia
3) Newly aquired
4) Being bullied
But since you only have the labs and they are juvis, I don't think they are being bullied because then the aggressor would still be out and about in the tank. My bet is that it's just because they are still becoming aquainted with the tank. Give it time and make sure you spend alot of time around the tank to get them acustomed to you.