Depends what's in the community tank... If it's only other mbuna and you feed the adults 1-2 times per day I find the young ones are fine at 1". Of those that are released by the females in the tank, the few that survive are usually left alone by the time they're 3/4" (but they're the smart ones ). I'd introduce them at lights out though and leave the lights off the next day. Obviously its best if there are plenty of small hiding spots in case they do feel at risk..